Partial coalescing of transmit buffers

ABSTRACT

The present invention facilitates overall system performance by balancing system resource utilization and network throughput. The invention analyzes packets received from host software selects one or more of buffers to coalesce into a single, coalesced buffer. The selection is based upon an initial fragment size selected to facilitate overall system performance. The coalesced buffer and non-coalesced buffers, are passed to a network device for transmission.

FIELD OF THE INVENTION

The present invention relates generally to network devices and systems,and more particularly, to systems and methods for coalescing transmitbuffers.

BACKGROUND OF THE INVENTION

Host-computing systems, such as personal computers, are often operatedas nodes on a communications network, where each node is capable ofreceiving data from the network and transmitting data to the network.Data is transferred over a network in groups or segments, wherein theorganization and segmentation of data are dictated by a networkoperating system protocol, and many different protocols exist. In fact,data segments that correspond to different protocols can co-exist on thesame communications network. In order for a node to receive and transmitinformation packets, the node is equipped with a peripheral networkinterface device, which is responsible for transferring informationbetween the communications network and the host system. Fortransmission, a processor unit in the host system constructs data orinformation packets in accordance with a network operating systemprotocol and passes them to the network peripheral. In reception, theprocessor unit retrieves and decodes packets received by the networkperipheral. The processor unit performs many of its transmission andreception functions in response to instructions from an interruptservice routine associated with the network peripheral. When a receivedpacket requires processing, an interrupt may be issued to the hostsystem by the network peripheral. The interrupt has traditionally beenissued after either all of the bytes in a packet or some fixed number ofbytes in the packet have been received by the network peripheral.

Networks are typically operated as a series or stack of layers orlevels, where each layer offers services to the layer immediately above.Many different layered network architectures are possible, where thenumber of layers, the function and content of each layer may bedifferent for different networks. The international standardsorganization (ISO) has developed an open systems interconnection (OSI)model defining a seven layer protocol stack including an applicationlayer (e.g., layer 7), a presentation layer, a session layer, atransport layer, a network layer, a data link layer, and a physicallayer (e.g., layer 1), wherein control is passed from one layer to thenext, starting at the application layer in one station, proceeding tothe bottom layer, over the channel to the next station and back up thehierarchy. The user of a host system generally interacts with a softwareprogram running at the uppermost (e.g., application) layer and thesignals are sent across the network at the lowest (e.g., physical)layer.

One popular network architecture is sometimes referred to as a TCP/IPstack, in which the application layer is one of FTP (file transferprotocol), HTTP (hyper text transfer protocol), or SSH (secure shell).In these networks, the transport layer protocol is typically implementedas transmission control protocol (TCP) or user datagram protocol (UDP),and the network layer employs protocols such as the internet protocol(IP), address resolution protocol (ARP), reverse address resolutionprotocol (RARP), or internet control message protocol (ICMP). The datalink layer is generally divided into two sublayers, including a mediaaccess control (MAC) sublayer that controls how a computer on thenetwork gains access to the data and permission to transmit it, as wellas a logical link control (LLC) sublayer that controls framesynchronization, flow control and error checking. The physical layerconveys the data as a bit stream of electrical impulses, light signals,and/or radio signals through the network at the physical (e.g.,electrical and mechanical) level. The physical layer implementsEthernet, RS232, asynchronous transfer mode (ATM), or other protocolswith physical layer components, where Ethernet is a popular local areanetwork (LAN) defined by IEEE 802.3.

One or more layers in a network protocol stack often provide tools forerror detection, including checksumming, wherein the transmittedmessages include a numerical checksum value typically computed accordingto the number of set bits in the message. The receiving network nodeverifies the checksum value by computing a checksum using the samealgorithm as the sender, and comparing the result with the checksum datain the received message. If the values are different, the receiver canassume that an error has occurred during transmission across thenetwork. In one example, the TCP and IP layers (e.g., layers 4 and 3,respectively) typically employ checksums for error detection in anetwork application.

Data may also be divided or segmented at one or more of the layers in anetwork protocol stack. For example, the TCP protocol provides fordivision of data received from the application layer into segments,where a header is attached to each segment. Segment headers containsender and recipient ports, segment ordering information, and achecksum. Segmentation is employed, for example, where a lower layerrestricts data messages to a size smaller than a message from an upperlayer. In one example, a TCP frame may be as large as 64 kbytes, whereasan Ethernet network may only allow frames of a much smaller size at thephysical layer. In this case, the TCP layer may segment a large TCPframe into smaller segmented frames to accommodate the size restrictionsof the Ethernet.

One or more of the network protocol layers may employ securitymechanisms such as encryption and authentication to prevent unauthorizedsystems or users from reading the data, and/or to ensure that the datais from an expected source. For instance, IP security (IPsec) standardshave been adopted for the IP layer (e.g., layer 3 of the OSI model) tofacilitate secure exchange of data, which has been widely used toimplement virtual private networks (VPNs). IPsec supports two operatingmodes, including transport mode and tunnel mode. In transport mode, thesender encrypts the data payload portion of the IP message and the IPheader is not encrypted, whereas in tunnel mode, both the header and thepayload are encrypted. In the receiver system, the message is decryptedat the IP layer, wherein the sender and receiver systems share a publickey through a security association (SA). Key sharing is typicallyaccomplished via an internet security association and key managementprotocol (ISAKMP) that allows the receiver to obtain a public key andauthenticate the sender using digital certificates.

The network protocol stack is operable to receive data or packets fromhost software, properly format the data, and pass the data to thenetwork device for transmission. Each packet sent requires separatebuffer or memory storage space, processing time for the network protocolstack to analyze and format as necessary, and processing time for thenetwork device to process the packet (e.g., analyze, segment, checksumgeneration, and the like). This processing of each packet is at leastpartially independent of the size of data within the packet, which canresult in a large amount of processing overhead for a given amount ofdata being transmitted, particularly form smaller sized packets.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basicunderstanding of one or more aspects of the invention. This summary isnot an extensive overview of the invention, and is neither intended toidentify key or critical elements of the invention, nor to delineate thescope thereof. Rather, the primary purpose of the summary is to presentsome concepts of the invention in a simplified form as a prelude to themore detailed description that is presented later.

The present invention facilitates network throughput by partiallycoalescing transmit buffers. Most network devices of today also functionas busmasters in that they have the ability to obtain data from systemmemory without substantial intervention by a host CPU (e.g., directmemory access (DMA)). This requires that a network driver providephysical address to buffers that holds data to the network device. Whena small amount of data is scattered in several buffers, performance cansuffer when the network device obtains the data stored within thebuffers. Additionally, performance can also suffer if all the data iscoalesced into a single buffer and obtained/passed by the networkdevice. The present invention analyzes packets received from hostsoftware, determines which/whether coalescing of the packets wouldfacilitate processing, and can coalesce the packets into largercontiguous buffers that improve throughput.

To the accomplishment of the foregoing and related ends, the inventioncomprises the features hereinafter fully described and particularlypointed out in the claims. The following description and the annexeddrawings set forth in detail certain illustrative aspects andimplementations of the invention. These are indicative, however, of buta few of the various ways in which the principles of the invention maybe employed. Other objects, advantages and novel features of theinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is block diagram illustrating transfer of data for network systemin accordance with an aspect of the present invention.

FIG. 2 is a flow diagram illustrating a method for partial coalescing oftransmit buffers in accordance with an aspect of the present invention.

FIG. 3 is block diagram illustrating an exemplary case partialcoalescing of transmit buffers in accordance with an aspect of thepresent invention.

FIG. 4 is block diagram illustrating an exemplary case partialcoalescing of transmit buffers in accordance with an aspect of thepresent invention.

FIG. 5 is a flow diagram illustrating a method for partial coalescing oftransmit buffers in accordance with an aspect of the present invention.

FIG. 6 is a flow diagram illustrating a method of coalescing a pluralityof transmit buffers in accordance with an aspect of the presentinvention.

FIG. 7 is a flow diagram illustrating another method of coalescing aplurality of transmit buffers in accordance with an aspect of thepresent invention.

FIG. 8 is a block diagram illustrating a high speed communicationnetwork system in accordance with an aspect of the present invention.

FIG. 9A is a schematic diagram illustrating another exemplary networkinterface system in which various aspects of the invention may becarried out.

FIG. 9B is a schematic diagram illustrating an exemplary single-chipnetwork controller implementation of the network interface system ofFIG. 9A.

FIG. 10 is a schematic diagram illustrating a host system interfacingwith a network using the exemplary network controller of FIG. 9B.

FIG. 11A is a schematic diagram illustrating a control status block in ahost system memory with pointers to descriptor rings and receive statusrings in the host system of FIG. 9A.

FIG. 11B is a schematic diagram illustrating a controller status blockin the host memory of the host system of FIG. 9A.

FIG. 11C is a schematic diagram illustrating descriptor management unitregisters in the network interface system of FIG. 9A.

FIG. 11D is a schematic diagram illustrating an exemplary transmitdescriptor ring in host system memory and pointer registers in adescriptor management unit of the network interface system of FIG. 9A.

FIG. 11E is a schematic diagram illustrating an exemplary transmitdescriptor in the network interface system of FIG. 9A.

FIG. 11F is a schematic diagram illustrating a transmit flags byte inthe transmit descriptor of FIG. 11E.

FIG. 11G is a schematic diagram illustrating an exemplary receivedescriptor in the network interface system of FIG. 9A.

FIG. 11H is a schematic diagram illustrating an exemplary receivedescriptor ring and receive status ring in host system memory, as wellas pointer registers in the descriptor management unit of the networkinterface system of FIG. 9A.

FIG. 11I is a schematic diagram illustrating an exemplary receive statusring in host system memory and pointer registers in the descriptormanagement unit in the network interface system of FIG. 9A.

FIG. 11J is a schematic diagram illustrating an exemplary receive statusring entry in the host system memory.

FIGS. 12A and 12B are schematic diagrams illustrating outgoing data fromTCP through transport mode ESP processing for IPv4 and IPv6,respectively.

FIGS. 12C and 12D are schematic diagrams illustrating outgoing data fromTCP through tunnel mode ESP processing for IPv4 and IPv6, respectively.

FIG. 12E is a schematic diagram illustrating exemplary ESP header, ESPtrailer, authentication data, and protected data.

FIGS. 13A and 13B are schematic diagrams illustrating exemplary TCPframe formats for IPv4 and IPv6, respectively.

FIGS. 14A and 14B are tables illustrating frame fields modified byoutgoing ESP and AH processing, respectively, in the network interfacesystem of FIG. 9A.

FIGS. 14C and 14D are schematic diagrams illustrating pseudo headerchecksum calculations for IPv4 and IPv6, respectively in the networkinterface system of FIG. 9B.

FIG. 15 is a schematic diagram illustrating security processing ofoutgoing data in the network interface system of FIG. 9B.

FIG. 16 is a schematic diagram illustrating security processing ofincoming network data in the network interface system of FIG. 9B.

FIG. 17A is a schematic diagram illustrating an exemplary securityassociation table write access in the network interface system of FIG.9B.

FIG. 17B is a schematic diagram illustrating an exemplary SA addressregister format in the network interface system of FIG. 9B.

FIG. 17C is a schematic diagram illustrating an exemplary SPI tableentry format in the network interface system of FIG. 9B.

FIG. 17D is a schematic diagram illustrating an exemplary SA memoryentry format in the network interface system of FIG. 9B.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with respect to theaccompanying drawings in which like numbered elements represent likeparts. The figures provided herewith and the accompanying description ofthe figures are merely provided for illustrative purposes. One ofordinary skill in the art should realize, based on the instantdescription, other implementations and methods for fabricating thedevices and structures illustrated in the figures and in the followingdescription, and such alternatives are contemplated as falling withinthe scope of the present invention.

Many network devices/controllers at least partially function asbusmasters in that they have a built in direct memory access (DMA)engine that allows them to obtain data from system memory withoutsubstantial intervention or involvement by a host processor. Thisrequires that a network device driver provide physical addresses of thebuffers within system memory that hold the data to the network device.However, when a relatively small amount of data is scattered in severalbuffers, performance can suffer when all of the “small” buffers areaccessed by the network device via DMA. In such situations, frames canconsist mainly of header information with very little data.Additionally, overall system performance can suffer when buffers areexcessively coalesced into a single buffer. Significant processingoverhead can be required to perform coalescing and can more than offsetnetwork throughput, thereby decreasing overall system performance. Theamount of processing overhead that can be used without decreasingoverall system performance can vary substantially and is dependent on anumber of factors such as, processor speed, system memory size, networkoperation data rates, and the like.

FIG. 1 is a block diagram illustrating transfer of data for a networksystem 100 in accordance with an aspect of the present invention. Thesystem 100 is described so as provide an overview of the presentinvention. The system 100 includes a network device 102, a networkdevice driver 104, host memory 106, and host software 108. The system100 is operable to transfer data to and receive data from a network 110(e.g., wireless, wired, cellular, combination, and the like). Furtherdetails of operation of the system 100 and similar systems are describedinfra.

Generally, operating systems send packets to network device drivers fortransmission. Network device drivers are processor executable codeand/or software that controls operation of network devices. The networkdevice drivers process the packets and provide or permit access to thepackets to network devices, which in turn transmit the packets on anetwork. Typically, each packet spans several buffers wherein headerinformation (e.g., source address, destination address, MAC header, IPheader, TCP header, and the like) arrives in separate buffers and thedata follows in one or more buffers. The device drivers provide orpermit access to the buffers to network devices. However, if the buffersare provided as is, network performance as well as system performancecan suffer due to buffer fragments (e.g., relatively small buffers). Thesystem 100 can mitigate loss of network throughput and can improveoverall system performance by combining a number of relatively smallerbuffers or fragments into a single, contiguous memory space referred toas a coalesced buffer. The operation of combining the number of buffersinto a single buffer is referred to as coalescing.

The network device 102 is responsible for physically transferring data,typically as frames, to and from the network 110. Frames generallycomprise a data packet along with at least some header information. Inorder to transmit data, the network device 102 retrieves frames from thehost memory 106, performs some processing on the frames (e.g., checksumgeneration, segmentation, encryption, decryption, and the like) and thenplaces the frames on the network 110. In order to receive data, thenetwork device 102 receives appropriately identified frames from thenetwork 110, performs some processing on the frames, and then placesthem in select locations in the host memory 106.

The network device driver 104 is operable to process the received frameslocated in the host memory 106 and pass (i.e., permit/provide access tothe memory locations in the host memory containing the received frames)them to the host software 108. Additionally, the driver 104 is operableto assemble frames for transmission based upon data and headerinformation received from or provided by the host software 108. Inaddition to the above transmit and receive operations, the driver 104 isfurther operable to perform other functions including, but not limitedto, network device initialization, configuration, and the like.

The host memory 106 is one or more contiguous locations within systemmemory, and is accessible by both the network device 102 and the driver104. The host software 108 includes software executable or executing ona computer system such as, an operating system, application software,and the like. The host software 108 determines when and what data tosend and where to send it (destination) as well as other optionalinformation. Additionally, the host software 108 can request data orreceive data from other computer systems on the network.

On receipt of one or more received frames, the network device 102processes and then places those frames at one or more specific locationsin the host memory 106 via a bus and/or DMA mechanism. The driver 104accesses the received frame(s) and processes the frames (e.g.,authenticating, error checking, and the like). Then, the driver 104passes the received data to the host software 108 in a host softwarecompatible format. It is appreciated that passing and/or receiving datais intended to include sending/receiving pointers to data and/or settingappropriate flags and is not limited to physically transferring data forthe present invention. The device driver 104 attempts to avoidphysically copying the received data from one location to another andmay supply pointers to memory locations located in the host memory 106that contain the received data. The host software 108 can then accessand process the received data as needed.

On transmit of one or more frames, the host software 108 notifies thedriver 104 of the data to be sent as well as header information for thedata. The host software 108 places the header information as well as thedata into one or more virtual buffers. Generally, virtual buffers map toone or more physical buffers. The driver 104 is operable to analyze thevirtual buffers where the packet is located as well as correspondingphysical buffers to determine whether to coalesce some of the virtualbuffers or associated physical buffers into a single coalesced buffer inorder to facilitate transmission. As an example, for an initial fragmentsize of 256 bytes, the driver 104 is operable to coalesce a number ofvirtual buffers into a single coalesced physical buffer less than orequal to 256 bytes. Additionally, the driver 104 manipulates the dataand the header information so as to assemble one or more transmit framesin a format compatible with the network device 102. The coalescedphysical buffer as well as non-coalesced physical buffers are madeaccessible to the network device (e.g., by setting a flag, descriptor,physical pointers, and the like). Then, the network device 102 accessesthe buffers, optionally performs additional processing on the frame, andtransmits the frame on the network 110.

While, for purposes of simplicity of explanation, the methodologies ofbelow are depicted and described as executing serially, it is to beunderstood and appreciated that the present invention is not limited bythe illustrated order, as some aspects could, in accordance with thepresent invention, occur in different orders and/or concurrently withother aspects from that depicted and described herein. Moreover, not allillustrated features may be required to implement a methodology inaccordance with an aspect the present invention.

Turning now to FIG. 2, a flow diagram illustrating a method 200 forpartial coalescing of transmit buffers in accordance with an aspect ofthe present invention is disclosed. The method 200 is typicallyperformed by or within a device driver operating on a computer system orstation. Generally, the method 200 analyzes buffers containinginformation for a packet and determines which buffers, if any, tocoalesce, thereby facilitating network throughput.

Physical buffers are storage space/locations in memory with a specifiedstarting address and a length or size. The starting address isreferenced by a physical pointer that points to a physical location inhost memory. Similarly, virtual buffers are also storage space/locationin memory with a specified starting address and a length or size.However, virtual buffers map to one or more physical memory locations orbuffers. Additionally, the starting address for a virtual buffer isreferenced by a virtual pointer that points to a virtual location invirtual memory. Virtual buffers are often employed in computers systemsfor a number of reasons including, but not limited to, convenience,control/protect of access to physical memory locations, and othersimilar reasons. However, devices such as network devices typicallyrequire physical memory locations and physical address pointers. Thus,virtual buffers employed for packets to be transmitted generally areconverted or copied into one or more physical buffers for use by networkdevices.

The method 200 begins at block 202 wherein a device driver,executable/executing program code, receives a packet from host software(e.g., operating system). It is appreciated that passing and/orreceiving data is intended to include sending/receiving pointers to dataand/or setting appropriate flags and is not limited to physicallytransferring data for the present invention. The received packet isstored in an array of virtual buffers that map to an array physicalbuffers. Each of the virtual buffers is associated with one or morebuffers of the array of physical buffers. At block 204, the array ofvirtual buffers and the array of physical buffers are analyzed andcompared to identify respective elements or buffers within each arrayand sizes of each buffer.

If the virtual buffer sizes exceed the physical buffer sizes, the method200 copies an initial number of the virtual buffers into a singlecoalesced physical buffer at block 206. The initial number of virtualbuffers copied is determined by their respective sizes. Generally, theseinitial number of virtual buffers have a total length less than or equalto a initial size or initial fragment size (e.g., 256 bytes). The valueor amount of this initial size can be determined through experimentationand/or dynamically derived based on system performance.

Otherwise, if the physical buffer sizes exceed the virtual buffer sizes,the method 200 analyzes the physical buffers to obtain a physicallength/size for each of the physical buffers at block 208. Then, aninitial number of the physical buffers are coalesced into the singlecoalesced physical buffer at block 210. Similarly, the initial number ofphysical buffers copied is determined by their respective sizes and havea size less than or equal to the initial size, discussed above.

Continuing at block 212, the coalesced physical buffer and non-coalescedphysical buffers are passed to a network device as an array via a directmemory access operation. The coalesced physical buffer and non-coalescedphysical buffers comprise a frame available for transmission. At thispoint, the network device can perform additional processing on the frameand then transmit the frame on a network.

FIG. 3 is a block diagram illustrating an exemplary case for partialcoalescing of transmit buffers wherein virtual buffer sizes exceedphysical buffer sizes in accordance with an aspect of the presentinvention. It is appreciated that the diagram is provided merely forillustrative purposes and that other buffer sizes and number of bufferscan be employed and present in accordance with the present invention.The diagram assumes an initial fragment size of about 256 bytes.

An array of physical buffer elements 301 and their corresponding sizesas well as an array of virtual buffers 302 and their corresponding sizesare depicted. From FIG. 3, it can be seen that a first virtual buffer310 maps to first and second physical buffers 311 and 312. In order toobtain a coalesced array of physical buffers 303, the first virtualbuffer having a size of 34 bytes and a second virtual buffer having asize of 20 bytes are copied to a coalesced buffer 313 having a size of54 bytes.

FIG. 4 is a block diagram illustrating an exemplary case for partialcoalescing of transmit buffers wherein the physical buffer sizes exceedthe virtual buffer sizes in accordance with an aspect of the presentinvention. Again, it is appreciated that the diagram is provided merelyfor illustrative purposes and that other buffer sizes and number ofbuffers can be employed and present in accordance with the presentinvention. The diagram assumes an initial fragment size of about 256bytes.

An array of physical buffer elements 401 and their corresponding sizesas well as an array of virtual buffers 402 and their corresponding sizesare depicted. Here, a fourth physical buffer 410 should be coalescedbecause the size of the physical buffers to that point is less than aninitial size of 256 bytes. Thus, a first, second, and third virtualbuffers 411, 412, and 413 should not simply be copied to a singlephysical buffer because coalescing the physical buffers increases thesize of the coalesced buffers and reduces the number of buffers in thecoalesced array.

The array of physical buffers 401 are parsed by a device driver, inorder, to obtain a physical coalesce length, which is the length or sizeof an initial number of physical buffers (154 here) less than a 256 byteinitial size. These initial physical buffers are coalesced into a singlephysical coalesced buffer 414 having a size of 154 bytes. It is notedthat merely coalescing the virtual buffers would yield a coalescedbuffer of only 54 bytes.

FIG. 5 is a flow diagram of a method 500 for partial coalescing transmitbuffers in accordance with an aspect of the present invention. Themethod 500 analyzes physical buffers associated with a packet and canpartially coalesce one or more of the physical buffers to facilitatetransmission. This method 500, in contrast to the method 200 of FIG. 2,operates with the physical buffers. The method 200 can be extended tooperate with virtual buffers by translating and/or mapping the virtualbuffers to physical buffers.

The method 500 begins at block 502 where a packet is received from hostsoftware, wherein the packet is located in an array (ordered) ofphysical buffers. Each physical buffer has a physical location in hostmemory and has a size associated therewith. An initial fragment size isdetermined and/or obtained at block 504. The initial fragment size is amaximum size or length for a coalesced buffer.

Subsequently, the method 500 analyzes one or more of the buffers in thearray, in order, at block 506 to select buffers to coalesce. A compositeor total length of these selected buffers should be less than or equalto the initial fragment size. The selected buffers can then be copied orcoalesced into a single coalesced buffer at block 508. The coalescedbuffer should be located in contiguous memory space so as to facilitatenetwork throughput. The selected buffers that have been coalesced can bemarked or identified as having been coalesced and can be freed and/orotherwise made available for other use by the computer system 510. Aswith the composite length of the selected buffers, the length of thecoalesced buffer should be less than or equal to the initial fragmentsize. A number of suitable mechanisms/methods can be employed inaccordance with the present invention in order to select buffers of thearray of buffers to coalesce and are discussed supra and infra. Acoalesced array comprising the coalesced buffer and non-coalescedbuffers of the original array is made available to a network device fortransmission at block 512.

FIG. 6 is a flow diagram of a method 600 for coalescing a plurality oftransmit buffers in accordance with an aspect of the invention.Generally, the method 600 selects buffers to coalesce from an array ofbuffers. It is appreciated that variations of the method that selectbuffers according to a fragment size are contemplated by the presentinvention.

The method 600 begins at block 602 where a fragment size is obtained.The fragment size limits the number and size of buffers to be coalesced.At block 604, an array of physical buffers that comprise headerinformation and data for a packet are obtained. Beginning with a firstbuffer in the array and iteratively proceeding in order therefrom, acomposite size is computed for a current buffer and compared with thefragment size at block 606. Initially, the composite size is typicallyequal to the size of the first buffer. Subsequently, the composite sizeis equal to the size of the current buffer and the size of a coalescedbuffer. If the composite size is less than the fragment size, thecurrent buffer is coalesced into the coalesced buffer that now has asize or length equal to the composite size at block 608. Otherwise, acoalesced array comprised of the coalesced buffer and non-coalescedbuffers of the array of physical buffers is generated. It is appreciatedthat the coalesced array can, in some operations, fail to have thecoalesced buffer present and/or can fail to have any non-coalescedbuffers present.

FIG. 7 is a flow diagram of a method 700 for coalescing a plurality oftransmit buffers in accordance with an aspect of the invention. Themethod 700 analyzes virtual buffers and physical buffers associated witha packet in order to generate a coalesced buffer and an array of bufferstherefrom.

At block 702, a packet located in an array of one or more virtualbuffers is obtained. The virtual buffers store header information anddata for the packet. The respective virtual buffers are mapped to anarray of one or more physical buffers at block 704. It is appreciatedthat the number of buffers located in the array of virtual buffers canvary from the number of buffers located in the array of physicalbuffers.

Sizes for the array of virtual buffers and the array of physical buffersare obtained at block 706. If the sizes of one or more virtual buffersare greater than the sizes of corresponding physical buffers, a numberof the virtual buffers are selected and coalesced into a coalescedbuffer at block 708. Physical buffers that correspond to the selectedvirtual buffer are deemed or considered to be coalesced buffers. Thecoalesced buffer is a physical buffer located in system memory.Alternately, if the sizes of one or more virtual buffers are less thanthe sizes of corresponding physical buffers, a number of the physicalbuffers are selected and coalesced into the coalesced buffer at block710. The coalesced buffer and non-coalesced physical buffers arecompiled into a coalesced array at block 712.

FIG. 8 is a block diagram illustrating a high speed communicationnetwork system 800 in accordance with an aspect of the presentinvention. The system 800 includes a network communication medium 802and a plurality of stations 804 or nodes that are connected via thenetwork medium 802. The stations 804 are computer or processor basedsystems that send and receive data according to one or more networkprotocols. The network medium 802 can be a combination of network typesincluding wireless, wired, cellular, and the like. Additionally, thesystem 800 is operable to transmit data at high speeds including, butnot limited to, about 10 Mbps to about 1 Gbps.

The system 800 is a carrier sense multiple access with collisiondetection (CSMA/CD) system typically employed in local area networks inthe medium access control (MAC) sublayer. The stations 804 operateindependently to transmit frames/data, receive frames/data, detectcollisions, and the like. The stations employ a device driver inaccordance with the present invention that partially coalesces transmitbuffers according to a determined fragment size. As a result, greaternetwork throughput in less frames can be achieved by this partialcoalescing. Additionally, the stations 804 are operable to dynamicallymodify the determined fragment size within a selected range. Asdescribed previously, significant processing overhead can be requiredfor coalescing buffers resulting in a tradeoff between processingoverhead and network throughput. The stations 804 can dynamicallydetermine the fragment size so as to improve/adjust overall systemperformance, which is dependent on both processing overhead and networkthroughput. For example, a station could increase the fragment size soas to improve network performance at the expense of processing overheador could decrease the fragment size so as to reduce processing overheadat the expense of network performance.

A structural/functional and operational overview of a network controllerin accordance with the present invention will be provided below in orderto facilitate a thorough understanding of the present invention. Datatransfer for the network controller described below can be improved byemploying the coalescing described supra.

FIG. 9A illustrates a network interface peripheral or network controller102 in accordance with one or more aspects of the present invention, andFIGS. 9B and 10 illustrate an exemplary single-chip implementation 102 aof the network controller 102. The exemplary single-chip networkcontroller 102 a includes all the functionality and components describedherein with respect to the network interface system 102. The variousblocks, systems, modules, engines, etc. described herein may beimplemented using any appropriate analog and/or digital circuitry,wherein one or more of the blocks, etc. described herein may be combinedwith other circuitry in accordance with the invention.

The network controller 102 includes a 64-bit PCI-X bus interface 104 forconnection with a host PCI or PCI-X bus 106 that operates at a clockspeed up to 133 MHz in PCI-X mode or up to 66 MHz in standard PCI mode.The network controller 102 may be operated as a bus master or a slave.Much of the initialization can be done automatically by the networkcontroller 102 when it reads an optional EEPROM (not shown), forexample, via an EEPROM interface 114 (FIG. 9B). The network controller102 can be connected to an IEEE 802.3 or proprietary network 108 throughan IEEE 802.3-compliant Media Independent Interface (MID or GigabitMedia Independent Interface (GMII) 110, for interfacing the controller102 with the network 108 via an external transceiver device 111. For1000 Mb/s operation the controller 102 supports either the byte-wideIEEE 802.3 Gigabit Media Independent Interface (GMII) for 1000BASE-T PHYdevices 111 or the IEEE 802.3 Ten-Bit Interface (TBI) for 1000BASE-Xdevices 111. The network controller 102 supports both half-duplex andfull-duplex operation at 10 and 100 Mb/s rates and full-duplex operationat 1000 Mb/s.

A host device, such as a host processor 112 on the host PCI-X bus 106 ina host system 180, may interface with the network controller 102 via thebus 106 and a host bridge 117. The host processor 112 includes one ormore processors that can operate in a coordinated fashion. Referringalso to FIG. 10, the network single-chip network controller 102 a may beprovided on a network interface card or circuit board 182, together witha PHY transceiver 111 for interfacing the host processor 112 with thenetwork 108 via the host bridge 117, the host bus 106, and thetransceiver 111. The PCI-X bus interface 104 includes PCI configurationregisters used to identify the network controller 102 a to other deviceson the PCI bus and to configure the device. Once initialization iscomplete, the host processor 112 has direct access to the I/O registersof the network controller 102 for performance tuning, selecting options,collecting statistics, and starting transmissions through the hostbridge 117 and the bus 106. The host processor 112 is operativelycoupled with the host system memory 128 and a cache memory 115 via amemory/cache controller 113. One or more application software programs184 executing in the host processor 112 may be provided with networkservice via layer 4 (e.g., transport layer) software, such astransmission control protocol (TCP) layer software 186, layer 3 (e.g.,network layer) software 188, such as internet protocol (IP) software188, and a software network driver 190, also running on the hostprocessor 112. As discussed below, the network driver software 190interacts with the host memory 128 and the network controller 102 tofacilitate data transfer between the application software 184 and thenetwork 108.

As illustrated in FIG. 9A, the exemplary network controller 102comprises first and second internal random access memories MEMORY A 116and MEMORY B 118, organized as first-in first-out (FIFO) memories forstorage of frames. A memory control unit 120 is provided for control andoperation of the memories 116 and 118. The network controller 102 alsocomprises a media access control (MAC) engine 122 satisfyingrequirements for operation as an Ethernet/IEEE 802.3—compliant node andproviding the interface between the memory 118 and the GMII 110. The MACengine 122 may be operated in full or half-duplex modes. An InternetProtocol Security (IPsec) engine 124 coupled with the memories 116 and118 provides authentication and/or encryption functions.

The PCI-X bus interface 104 includes a Direct Memory Access (DMA)controller 126 that automatically transfers network frame data betweenthe network controller 102 and buffers in host system memory 128 via thehost bus 106. The operation of the DMA controller 126 is directed by adescriptor management unit 130 according to data structures calleddescriptors 192, which include pointers to one or more data buffers 194in system memory 128, as well as control information. The descriptors192 are stored in the host system memory 128 in queues called descriptorrings. Four transmit descriptor rings are provided for transmittingframes and four'receive descriptor rings for receiving frames,corresponding to four priorities of network traffic in the illustratedcontroller 102. Additionally, four receive status rings are provided,one for each priority level, that facilitate synchronization between thenetwork controller 102 and the host system. Transmit descriptors 192control the transfer of frame data from the system memory 128 to thecontroller 102, and receive descriptors 192 control the transfer offrame data in the other direction. In the exemplary controller 102, eachtransmit descriptor 192 corresponds to one network frame, whereas eachreceive descriptor 192 corresponds to one or more host memory buffers inwhich frames received from the network 108 can be stored.

The software interface allocates contiguous memory blocks fordescriptors 192, receiver status, and data buffers 194. These memoryblocks are shared between the software (e.g., the network driver 190)and the network controller 102 during normal network operations. Thedescriptor space includes pointers to network frame data in the buffers194, the receiver status space includes information passed from thecontroller 102 to the software in the host 112, and the data bufferareas 194 for storing frame data that is to be transmitted (e.g.,outgoing data) and for frame data that has been received (e.g., incomingdata).

Synchronization between the controller 102 and the host processor 112 ismaintained by pointers stored in hardware registers 132 in thecontroller 102, pointers stored in a controller status block (CSB) 196in the host system memory 128, and interrupts. The CSB 196 is a block ofhost system memory 128 that includes pointers into the descriptor andstatus rings and a copy of the contents of the controller's interruptregister. The CSB 196 is written by the network controller 102 and readby the host processor 112. Each time the software driver 190 in the host112 writes a descriptor or set of descriptors 192 into a descriptorring, it also writes to a descriptor write pointer register in thecontroller 102. Writing to this register causes the controller 102 tostart the transmission process if a transmission is not already inprogress. Once the controller has finished processing a transmitdescriptor 192, it writes this information to the CSB 196. Afterreceiving network frames and storing them in receive buffers 194 of thehost system memory 128, the controller 102 writes to the receive statusring and to a write pointer, which the driver software 190 uses todetermine which receive buffers 194 have been filled. Errors in receivedframes are reported to the host memory 128 via a status generator 134.

The IPsec module or engine 124 provides standard authentication,encryption, and decryption functions for transmitted and receivedframes. For authentication, the IPsec module 124 implements theHMAC-MD5-96 algorithm defined in RFC 2403 (a specification set by theInternet Engineering Task Force) and the HMAC-SHA-1-96 algorithm definedin RFC 2404. For encryption, the module implements the ESP DES-CBC (RFC2406), the 3DES-CBC, and the AES-CBC encryption algorithms. Fortransmitted frames, the controller 102 applies IPsec authenticationand/or encryption as specified by Security Associations (SAs) stored ina private local SA memory 140, which are accessed by IPsec system 124via an SA memory interface 142. SAs are negotiated and set by the hostprocessor 112. SAs include IPsec keys, which are required by the variousauthentication, encryption, and decryption algorithms, IPsec keyexchange processes are performed by the host processor 112. The host 112negotiates SAs with remote stations and writes SA data to the SA memory140. The host 112 also maintains an IPsec Security Policy Database (SPD)in the host system memory 128.

A receive (RX) parser 144 associated with the MAC engine 122 examinesthe headers of received frames to determine what processing needs to bedone. If it finds an IPsec header, it uses information contained in theheader, including a Security Parameters Index (SPI), an IPsec protocoltype, and an IP destination address to search the SA memory 140 using SAlookup logic 146 and retrieves the applicable security association. Theresult is written to an SA pointer FIFO memory 148, which is coupled tothe lookup logic 146 through the SA memory interface 142. The keycorresponding to the SA is fetched and stored in RX key FIFO 152. Areceive (RX) IPsec processor 150 performs the processing requires by theapplicable SA using the key. The controller 102 reports what securityprocessing it has done, so that the host 112 can check the SPD to verifythat the frame conforms with policy. The processed frame is stored inthe memory 116.

A receive IPsec parser 154, associated with IPsec processor 150,performs parsing that cannot be carried out before packet decryption.Some of this information is used by a receive (Rx) checksum and padcheck system 156, which computes checksums specified by headers that mayhave been encrypted and also checks pad bits that may have beenencrypted to verify that they follow a pre-specified sequence for padbits. These operations are carried out while the received frame ispassed to the PCI-X bus 104 via FIFO 158. The checksum and pad checkresults are reported to the status generator 134.

In the transmit path, an assembly RAM 160 is provided to accept framedata from the system memory 128, and to pass the data to the memory 116.The contents of a transmit frame can be spread among multiple databuffers 194 in the host memory 128, wherein retrieving a frame mayinvolve multiple requests to the system memory 128 by the descriptormanagement unit 130. These requests are not always satisfied in the sameorder in which they are issued. The assembly RAM 160 ensures thatreceived chunks of data are provided to appropriate locations in thememory 116. For transmitted frames, the host 112 checks the SPD (IPsecSecurity Policy Database) to determine what security processing isneeded, and passes this information to the controller 102 in the frame'sdescriptor 192 in the form of a pointer to the appropriate SA in the SAmemory 140. The frame data in the host system memory 128 provides spacein the IPsec headers and trailers for authentication data, which thecontroller 102 generates. Likewise, space for padding (to make thepayload an integral number of blocks) is provided when the frame isstored in the host system memory buffers 194, but the pad bits arewritten by the controller 102.

As the data is sent out from the assembly RAM 160, it passes also into afirst transmit (TX) parser 162, which reads the MAC header, the IPheader (if present), the TCP or UDP header, and determines what kind ofa frame it is, and looks at control bits in the associated descriptor.In addition, the data from the assembly RAM 160 is provided to atransmit checksum system 164 for computing IP header and/or TCPchecksums, which values will then be inserted at the appropriatelocations in the memory 116. The descriptor management unit 130 sends arequest to the SA memory interface 142 to fetch an SA key, which is thenprovided to a key FIFO 172 that feeds a pair of TX IPsec processors 174a and 174 b. Frames are selectively provided to one of a pair of TXIPsec processors 174 a and 174 b for encryption and authentication viaTX IPsec FIFOs 176 a and 176 b, respectively, wherein a transmit IPsecparser 170 selectively provides frame data from the memory 116 to aselected one of the processors 174. The two transmit IPsec processors174 are provided in parallel because authentication processing cannotbegin until after encryption processing is underway. By using the twoprocessors 174, the speed is comparable to the receive side where thesetwo processes can be carried out simultaneously.

Authentication does not cover mutable fields, such as occur in IPheaders. The transmit IPsec parser 170 accordingly looks for mutablefields in the frame data, and identifies these fields to the processors174 a and 174 b. The output of the processors 174 a and 174 b isprovided to the second memory 118 via FIFOs 178 a and 178 b,respectively. An Integrity Check Value (ICV), which results fromauthentication processing, is inserted into the appropriate IPsec headerby an insertion unit 179 as the frame data is passed from the memory 118to the MAC engine 122 for transmission to the network 108.

In the single-chip implementation of FIG. 9B, the controller 102 acomprises a network port manager 182, which may automatically negotiatewith an external physical (PHY) transceiver via management data clock(MDC) and management data I/O (MDIO) signals. The network port manager175 may also set up the MAC engine 122 to be consistent with thenegotiated configuration. Circuit board interfacing for LED indicatorsis provided by an LED controller 171, which generates LED driver signalsLED0′-LED3′ for indicating various network status information, such asactive link connections, receive or transmit activity on the network,network bit rate, and network collisions. Clock control logic 173receives a free-running 125 MHz input clock signal as a timing referenceand provides various clock signals for the internal logic of thecontroller 102 a.

A power management unit 188, coupled with the descriptor management unit130 and the MAC engine 122, can be used to conserve power when thedevice is inactive. When an event requiring a change in power level isdetected, such as a change in a link through the MAC engine 122, thepower management unit 188 provides a signal PME′ indicating that a powermanagement event has occurred. The external serial EEPROM interface 114implements a standard EEPROM interface, for example, the 93Cxx EEPROMinterface protocol. The leads of external serial EEPROM interface 114include an EEPROM chip select (EECS) pin, EEPROM data in and data out(EEDI and EEDO, respectively) pins, and an EEPROM serial clock (EESK)pin.

In the bus interface unit 104, address and data are multiplexed on businterface pins AD[63:0]. A reset input RST′ may be asserted to cause thenetwork controller 102 a to perform an internal system reset. A cycleframe I/O signal FRAME∝ is driven by the network controller when it isthe bus master to indicate the beginning and duration of a transaction,and a PCI clock input PCI_CLK is used to drive the system bus interfaceover a frequency range of 15 to 133 MHz on the PCI bus (e.g., host bus106). The network controller 102 a also supports Dual Address Cycles(DAC) for systems with 64-bit addressing, wherein low order address bitsappear on the AD[31:0] bus during a first clock cycle, and high orderbits appear on AD[63:32] during the second clock cycle. A REQ64′ signalis asserted by a device acting as bus master when it wants to initiate a64-bit data transfer, and the target of the transfer asserts a 64-bittransfer acknowledge signal ACK64′ to indicate that it is willing totransfer data using 64 bits. A parity signal PAR64 is an even 8 byteparity signal that protects AD[63:32] The bus master drives PAR64 foraddress and write data phases and the target drives PAR64 for read dataphases.

The network controller 102 a asserts a bus request signal REQ′ toindicate that it wishes to become a bus master, and a bus grant inputsignal GNT′ indicates that the access to the bus has been granted to thenetwork controller. An initialization device select input signal IDSELis used as a chip select for the network controller during configurationread and write transactions. Bus command and byte enable signalsC/BE[7:0] are used to transfer bus commands and to indicate whichphysical bytes of data lines AD[63:0] carry meaningful data. A parityI/O signal PAR indicates and verifies even parity across AD[31:0] andC/BE[3:0].

The network controller drives a drive select I/O signal DEVSEL′ when itdetects a transaction that selects the network controller 102 a as atarget. The network controller 102 a checks DEVSEL′ to see if a targethas claimed a transaction that the network controller initiated. TRDY′is used to indicate the ability of the target of the transaction tocomplete the current data phase, and IRDY′ indicates the ability of theinitiator of the transaction to complete the current data phase.Interrupt request output signal INTA′ indicates that one or more enabledinterrupt flag bits are set. The network controller 102 a asserts aparity error I/O signal PERR′ when it detects a data parity error, andasserts a system error output signal SERR′ when it detects an addressparity error. In addition, the controller 102 a asserts a stop I/Osignal STOP′ to inform the bus master to stop the current transaction.

In the MAC engine 122, a physical interface reset signal PHY_RST is usedto reset the external PHY 111 (MII, GMII, TBI), a PHY loop-back outputPHY_LPBK is used to force an external PHY device 111 into loop-back modefor systems testing, and a flow control input signal FC controls whenthe MAC transmits a flow control frame. The network controller 102 aprovides an external PHY interface 110 that is compatible with eitherthe Media Independent Interface (MID, Gigabit Media IndependentInterface (GMII), or Ten Bit Interface (TBI) per IEEE Std 802.3. Receivedata input signals RXD[7:0] and output signals TXD[7:0] are used forreceive and transmit data exchange, respectively. When the networkcontroller 102 a is operating in GMII or MII mode, TX_EN/TXD[8] is usedas a transmit enable. In TBI mode, this signal is bit 8 of the transmitdata bus. RX_DV/RXD[8] is an input used to indicate that valid receivedata is being presented on the RX pins. In TBI mode, this signal is bit8 of the receive data bus.

When the network controller 102 a is operating in GMII or MII mode, RXER/RXD[9] is an input that indicates that the external transceiverdevice has detected a coding error in the receive frame currently beingtransferred on the RXD pins. In TBI mode, this signal is bit 9 of thereceive data bus. MII transmit clock input TX_CLK is a continuous clockinput that provides the timing reference for the transfer of the TX_ENand TXD[3:0] signals out of the network controller 102 a in MII mode.GTX_CLK is a continuous 125 MHz clock output that provides the timingreference for the TX_EN and TXD signals from the network controller whenthe device is operating in GMII or TBI mode. RX_CLK is a clock inputthat provides the timing reference for the transfer of signals into thenetwork controller when the device is operating in MII or GMII mode. COLis an input that indicates that a collision has been detected on thenetwork medium, and a carrier sense input signal CRS indicates that anon-idle medium, due either to transmit or receive activity, has beendetected (CRS is ignored when the device is operating in full-duplexmode). In TBI mode, 10-bit code groups represent 8-bit data packets.Some 10-bit code groups are used to represent commands. The occurrenceof even and odd code groups and special sequences called commas are allused to acquire and maintain synchronization with the PHY 110. RBCLK[0]is a 62.5 MHz clock input that is used to latch odd-numbered code groupsfrom the PHY device, and RBCLK[1] is used to latch even-numbered codegroups. RBCLK[1] is always 180 degrees out of phase with respect toRBCLK[0]. COM_DET is asserted by an external PHY 111 to indicate thecode group on the RXD[9:0] inputs includes a valid comma.

The IPsec module 124 includes an external RAM interface to memories 116and 118. When CKE is driven high, an internal RAM clock is used toprovide synchronization, otherwise the differential clock inputs CK andCK_L are used. The RAM's have a command decoder, which is enabled when achip select output CS_L is driven low. The pattern on the WE_L, RAS_L,and CAS_L pins defines the command that is being issued to the RAM. Bankaddress output signals BA[1:0] are used to select the memory to which acommand is applied, and an address supplied by RAM address output pinsA[10:0] selects the RAM word that is to be accessed. A RAM data strobeI/O signal DQS provides the timing that indicates when data can be reador written, and data on RAM data I/O pins DQ[31:0] are written to orread from either memory 116 or 118.

Returning again to FIG. 8, an operational discussion of receive andtransmit operation of the network controller 102 is provided below.Starting with receipt of a data frame from the network media 108 (e.g.,an optical fiber), the frame is delivered to the GMII 110 (the GigabitMedia-Independent Interface), for example, as a series of bytes or wordsin parallel. The GMII 110 passes the frame to the MAC 122 according toan interface protocol, and the MAC 122 provides some frame managementfunctions. For example, the MAC 122 identifies gaps between frames,handles half duplex problems, collisions and retries, and performs otherstandard Ethernet functions such as address matching and some checksumcalculations. The MAC 122 also filters out frames, checks theirdestination address and accepts or rejects the frame depending on a setof established rules.

The MAC 122 can accept and parse several header formats, including forexample, IPv4 and IPv6 headers. The MAC 122 extracts certain informationfrom the frame headers. Based on the extracted information, the MAC 122determines which of several priority queues (not shown) to put the framein. The MAC places some information, such as the frame length andpriority information, in control words at the front of the frame andother information, such as whether checksums passed, in status words atthe back of the frame. The frame passes through the MAC 122 and isstored in the memory 118 (e.g., a 32 KB RAM). In this example, theentire frame is stored in memory 118. The frame is subsequentlydownloaded to the system memory 128 to a location determined by thedescriptor management unit 130 according to the descriptors 192 in thehost memory 128 (FIG. 10), wherein each receive descriptor 192 comprisesa pointer to a data buffer 194 in the system memory 128. Transmitdescriptors include a pointer or a list of pointers, as will bediscussed in greater detail supra. The descriptor management unit 130uses the DMA 126 to read the receive descriptor 192 and retrieve thepointer to the buffer 194. After the frame has been written to thesystem memory 128, the status generator 134 creates a status word andwrites the status word to another area in the system memory 128, whichin the present example, is a status ring. The status generator 134 theninterrupts the processor 112. The system software (e.g., the networkdriver 190 in FIG. 10) can then check the status information, which isalready in the system memory 128. The status information includes, forexample, the length of the frame, what processing was done, and whetheror not the various checksums passed.

In transmit operation, the host processor 112 initially dictates a frametransmission along the network 108, and the TCP layer 186 of theoperating system (OS) in the host processor 112 is initiated andestablishes a connection to the destination. The TCP layer 186 thencreates a TCP frame that may be quite large, including the data packetand a TCP header. The IP layer 188 creates an IP header, and an Ethernet(MAC) header is also created, wherein the data packet, and the TCP, IP,and MAC headers may be stored in various locations in the host memory128. The network driver 190 in the host processor 112 may then assemblethe data packet and the headers into a transmit frame, and the frame isstored in one or more data buffers 194 in the host memory 128. Forexample, a typical transmit frame might reside in four buffers 194: thefirst one containing the Ethernet or MAC header, the second one havingthe IP header, the third one the TCP header, and the fourth buffercontaining the data. The network driver 190 generates a transmitdescriptor 192 that includes a list of pointers to all these databuffers 194.

The frame data is read from the buffers 194 into the controller 102. Toperform this read, the descriptor management unit 130 reads the transmitdescriptor 192 and issues a series of read requests on the host bus 106using the DMA controller 126. However, the requested data portions maynot arrive in order they were requested, wherein the PCI-X interface 104indicates to the DMU 130 the request with which the data is associated.Using such information, the assembly RAM logic 160 organizes andproperly orders the data to reconstruct the frame, and may also performsome packing operations to fit the various pieces of data together andremove gaps. After assembly in the assembly RAM 160, the frame is passedto the memory 116 (e.g., a 32 KB RAM in the illustrated example). As thedata passes from the assembly RAM 160, the data also passes to the TXparser 162. The TX parser 162 reads the headers, for example, the MACheaders, the IP headers (if there is one), the TCP or UDP header, anddetermines what kind of a frame it is, and also looks at the controlbits that were in the associated transmit descriptor 192. The data frameis also passed to the transmit checksum system 164 for computation ofTCP and/or IP layer checksums.

The transmit descriptor 192 may comprise control information, includingbits that instruct the transmit checksum system 164 whether to computean IP header checksum and/or TCP checksum. If those control bits areset, and the parser 162 identifies or recognizes the headers, then theparser 162 tells the transmit checksum system 164 to perform thechecksum calculations, and the results are put at the appropriatelocation in the frame in the memory 116. After the entire frame isloaded in the memory 116, the MAC 122 can begin transmitting the frame,or outgoing security processing (e.g., encryption and/or authentication)can be performed in the IPsec system 124 before transmission to thenetwork 108.

By offloading the transmit checksumming function onto the networkcontroller 102 of the present invention, the host processor 112 isadvantageously freed from that task. In order for the host processor 112to perform the checksum, significant resources must be expended.Although the computation of the checksum is relatively simple, thechecksum, which covers the entire frame, must be inserted at thebeginning of the frame. In conventional architectures, the host computermakes one pass through the frame to calculate the checksum, and theninserts the checksum at the beginning of the frame. The data is thenread another time as it is loaded into the controller. The networkcontroller 102 further reduces the load on the host processor 112 byassembling the frame using direct access to the system memory 128 viathe descriptors 192 and the DMA controller 126. Thus, the networkcontroller 102 frees the host processor 112 from several time consumingmemory access operations.

In addition to the receive and transmit functions identified above, thenetwork controller 102 may also be programmed to perform varioussegmentation functions during a transmit operation. For example, the TCPprotocol allows a TCP frame to be as large as 64,000 bytes. The Ethernetprotocol does not allow data transfers that large, but instead limits anetwork frame to about 1500 bytes plus some headers. Even in theinstance of a jumbo frame option that allows 16,000 byte network frames,the protocol does not support a 64 KB frame size. In general, a transmitframe initially resides in one or more of the data buffers 194 in systemmemory 128, having a MAC header, an IP header, and a TCP header, alongwith up to 64 KB of data. Using the descriptor management unit 130, theframe headers are read, and an appropriate amount of data (as permittedby the Ethernet or network protocol) is taken and transmitted. Thedescriptor management unit 130 tracks the current location in the largerTCP frame and sends the data block by block, each block having its ownset of headers.

For example, when a data transmit is to occur, the host processor 112writes a descriptor 192 and informs the controller 102. The descriptormanagement unit 130 receives a full list of pointers, which identify thedata buffers 194, and determines whether TCP segmentation is warranted.The descriptor management unit 130 then reads the header buffers anddetermines how much data can be read. The headers and an appropriateamount of data are read into the assembly RAM 160 and the frame isassembled and transmitted. The controller 102 then re-reads the headersand the next block or portion of the untransmitted data, modifies theheaders appropriately and forms the next frame in the sequence. Thisprocess is then repeated until the entire frame has been sent, with eachtransmitted portion undergoing any selected security processing in theIPsec system 124.

The network controller 102 of the present invention also advantageouslyincorporates IPSec processing therein. In contrast with conventionalsystems that offload IPSec processing, the present invention employson-board IPSec processing, which may be implemented as a single-chipdevice 102 a (FIG. 9B). In conventional systems, either the hostprocessor carries out IPSec processing or a co-processor, separate fromthe network controller, is employed. Use of the host processor is veryslow, and in either case, the frame passes at least three times throughthe memory bus. For example, when a co-processor is used, the framepasses through the bus once as it is read from memory and sent to theco-processor, again as it passes back to the system memory, and a thirdtime as it is sent to the network controller. This processing consumessignificant bandwidth on the PCI bus and negatively impacts systemperformance. A similar performance loss is realized in the receivedirection.

IPSec processing has two primary goals: first is to encrypt, orscramble, the data so that an unauthorized person or system cannot readthe data. The second goal is authentication, which ensures that thepacket is uncorrupted and that the packet is from the expected person orsystem. A brief discussion of the on-board IPSec processing followsbelow. The network controller 102 of the present invention takesadvantage of security associations (SAs) using the SA memory interface142, the SA lookup 146, and the SA memory 140. As briefly highlightedabove, a security association is a collection of bits that describe aparticular security protocol, for example, whether the IPSec portion 124is to perform an encryption or authentication, or both, and furtherdescribes what algorithms to employ. There are several standardencryption and authentication algorithms, so the SA interface 142 and SAlookup 146 indicates which one is to be used for a particular frame. TheSA memory 140 in the present example is a private memory, which storesthe encryption keys. The SAs are obtained according to an IPSec protocolwhereby sufficient information is exchanged with a user or system on thenetwork to decide which algorithms to use and allow both parties togenerate the same keys. After the information exchange is completed, thesoftware calls the driver 190, which writes the results into the SAmemory 140.

Once the key exchange is complete, the appropriate bits reside in the SAmemory 140 that indicate which key is to be used and whichauthentication algorithm, as well as the actual keys. In transmit mode,part of the descriptor 192 associated with a given outgoing frameincludes a pointer into the SA memory 140. When the descriptormanagement unit 130 reads the descriptor 192, it sends a request to theSA memory interface 142 to fetch the key, which then sends the key tothe key FIFO 172, that feeds the TX IPSec processing modules 174 a and174 b, respectively. When both encryption and authentication are to beemployed in transmit, the process is slightly different because thetasks are not performed in parallel. The authentication is a hash of theencrypted data, and consequently, the authentication waits until atleast a portion of the encryption has been performed. Because encryptionmay be iterative over a series of data blocks, there may be a delaybetween the beginning of the encryption process and the availability ofthe first encrypted data. To avoid having this delay affect deviceperformance, the exemplary network interface 102 employs two TX IPSecprocess engines 174 a and 174 b, wherein one handles the odd numberedframes and the other handles the even numbered frames in the illustratedexample.

Prior to performing the IPSec processing, the TX IPsec parser 170 parsesthe frame headers and looks for mutable fields therein, which are fieldswithin the headers that are not authenticated because they vary as theframe travels over the network 108. For example, the destination addressin the IP header varies as the frame goes across the Internet fromrouter to router. The transmit IPsec parser 170 identifies the mutablefields and passes the information to the TX IPSec processors 174, whichselectively skip over the mutable field portions of the frames. Theprocessed frames are sent to FIFOs 178 a and 178 b and subsequentlyaccumulated in the memory 118. The result of the authenticationprocessing is an integrity check value (ICV), which is inserted byinsertion block 179 into the appropriate IPsec header as the frame istransmitted from the memory 118 to the network media 108.

In receive mode, a received frame comes into the MAC 122 and the RXparser 144. The RX parser 144 parses the incoming frame up to the IPsecheaders and extracts information therefrom. The fields that areimportant to the RX parser 144 are, for example, the destination IPaddress in the PP header, the SPI (Security Protocol Index), and aprotocol bit that indicates whether an IPSec header is an authenticationheader(AH) or an encapsulation security protocol (ESP) header. Some ofthe extracted information passes to the SA lookup block 146. The SAlookup block 146 identifies the appropriate SA and conveys theinformation to the SA memory interface 142 that retrieves the SA andplaces it into the key FIFO 152.

The SA lookup block 146 employs an on-chip SPI Table and the off-chip SAmemory 140. The SPI Table is organized into 4096 bins, each comprising 4entries. The entries include the 32-bit SPI, a hash of the destinationaddress (DA), a bit to indicate the protocol, and a bit to indicatewhether the entry is used. Corresponding entries in the SA memorycontain the full DAs and the SA (two SAs when there is bothauthentication and encryption). The bin for each entry is determined bya hash of the SPI. To look up an SA, a hash of the SPI from the receivedframe is used to determine which bin to search. Within the bin, the SAlookup block 146 searches the entries for a match to the full SPI, thedestination address hash, and the protocol bit. After searching, the SAlookup block writes an entry to the SA pointer FIFO 148, which eitheridentifies a matching entry or indicates no match was found. A check ofthe DA address from the SA memory is made just before securityprocessing. If there is no match, security processing is not performedon the frame in question. Based on the entries in the SA pointer FIFO148, the keys are fetched from the external SA memory 140 and placed inthe key FIFO 152. The RX IPSec processor 150 takes the keys that come infrom the FIFO 152, reads the corresponding frame data out of the memory118, and begins processing the frame, as required. For receiveprocessing, decryption and authentication proceed in parallel (onreceive, decryption and authentication are not sequential processes),and thus in this example only one RX IPSec processor is used.

The RX IPsec parser 154 parses the headers that follow the ESP header.Any header that follows the ESP header will be encrypted and cannot beparsed until decryption has taken place. This parsing must be completedbefore TCP/UDP checksums can be computed and before pad bits can bechecked. The decrypted data is stored in the memory 116. To perform theTCP/UDP checksums and pad checks without having to store the frame dataanother time, these functions are carried out by checksum and pad checksystem 156 while the data is being transferred from the memory 116 tothe host memory 128. In addition to the on-board IPSec processing andTCP segmentation highlighted above, the network controller 102 alsoprovides performance improvements in the execution of interrupts. Readlatencies are large when a host processor is required to read a registerfrom a network device. These latencies negatively impact systemperformance. In particular, as the host processor clock speed continuesto increase, the disparity between the clock speed and the time it takesto get a response from a network controller over a PCI or other host busbecomes larger. Accordingly, when a host processor needs to read from anetwork device, the processor must wait a greater number of clockcycles, thereby resulting in opportunity loss.

The network interface 102 avoids many read latencies by replacing readoperations with write operations. Write operations are not asproblematic because they can take place without involving the processor112. Thus when write information is sent to a FIFO, as long as thewrites are in small bursts, the network controller 102 can take thenecessary time to execute the writes without negatively loading theprocessor. To avoid read operations during a transmit operation, thedriver creates a descriptor 192 in the system memory 128 and then writesa pointer to that descriptor to the register 132 of the networkcontroller 102. The DMU 130 of the controller 102 sees the contents inthe register 132 and reads the necessary data directly from the systemmemory 128 without further intervention of the processor 112. Forreceive operations, the driver software 190 identifies empty buffers 194in the system memory 128, and writes a corresponding entry to theregister 132. The descriptor management unit 130 writes to pointers inthe transmit descriptor rings to indicate which transmit descriptors 192have been processed and to pointers in the status rings to indicatewhich receive buffers 194 have been used.

Unlike conventional architectures that require a host processor to readan interrupt register in the network controller, the present inventiongenerates and employs a control status block (CSB) 196 located in apredetermined region of the system memory 128 (e.g., a locationdetermined upon initialization). The network controller 102 writes tothe CSB 196 any register values the system needs. More particularly,after a frame has been completely processed, prior to generating aninterrupt, the network controller 102 writes a copy of the interruptregister to the CSB 196. Then the controller 102 asserts the interrupt;thus when the host processor 112 sees the interrupt in the register 132,the received data is already available in the receive data buffer 194.

Various operational and structural details of the exemplary networkinterface controller 102 are hereinafter provided in conjunction withthe figures. In particular, details of the descriptor managementfeatures, transmit data frame segmentation and checksumming, as well assecurity processing are illustrated and described below in greaterdetail to facilitate an understanding of the present invention in thecontext of the exemplary controller 102.

Descriptor Management

Referring now to FIGS. 8, 10, and 11A-11J, further details of thedescriptors 192 and the operation of the exemplary controller 102 areillustrated and described below. FIG. 11A illustrates the host memory128, including the controller status block (CSB) 196, frame data buffers194, an integer number ‘n’ descriptor rings DR1 . . . DRn for transmitand receive descriptors 192, and an integer number ‘m’ receive statusrings 199 RSR1 . . . RSRm. The transmit and receive descriptors 192 arestored in queues referred to herein as descriptor rings DR, and the CSB196 includes descriptor ring pointers DR_PNTR1 . . . DR_PNTRn to thedescriptor rings DR. In the exemplary controller 102, four transmitdescriptor rings are provided for transmitted frames and four receivedescriptor rings are provided for received frames, corresponding to fourpriorities of network traffic. Each descriptor ring DR in thisimplementation is treated as a continuous ring structure, wherein thefirst memory location in the ring is considered to come just after thelast memory location thereof. FIG. 11B illustrates pointers and othercontents of the exemplary CSB 196 and FIG. 11C illustrates variouspointer and length registers 132 in the controller 102. FIG. 11Dillustrates further details of an exemplary transmit descriptor ring,FIG. 11H and FIG. 11I show details relating to exemplary receivedescriptor and receive status rings, respectively. FIGS. 11E and 11Fillustrate an exemplary transmit descriptor, FIG. 11G illustrates anexemplary receive descriptor, and FIG. 11J illustrates an exemplaryreceive status ring entry.

As shown in FIG. 11A, the descriptors 192 individually include pointersto one or more data buffers 194 in the system memory 128, as well ascontrol information, as illustrated in FIGS. 11E-11G. Synchronizationbetween the controller 102 and the software driver 190 is provided bypointers stored in the controller registers 132, pointers stored in theCSB 196 in the system memory 128, and interrupts. In operation, thedescriptor management unit 130 in the controller 102 reads thedescriptors 192 via the DMA controller 126 of the bus interface 104 inorder to determine the memory location of the outgoing frames to betransmitted (e.g., in the data buffers 194) and where to store incomingframes received from the network 108. The CSB 196 is written by thenetwork controller 102 and read by the driver 190 in the host processor112, and the descriptor management registers 132 are written by thedriver 190 and read by the descriptor management unit 130 in thecontroller 102. The exemplary descriptor system generally facilitatesinformation exchange regarding transmit and receive operations betweenthe software driver 190 and the controller 102.

Referring now to FIG. 11B, the exemplary CSB 196 includes pointers intothe descriptor and status rings, as well as a copy of the contents ofthe controller's interrupt register. Transmit pointers TX_RD_PTR0through TX_RD_PTR3 are descriptor read pointers corresponding totransmit priorities 3 through 0, respectively, which point just beyondthe last 64-bit quad word (QWORD) that the controller 102 has read fromthe corresponding priority transmit descriptor ring. Receive statuspointers STAT_WR_PTR0 through STAT_WR_PTR3 are descriptor write pointerscorresponding to transmit priorities 3 through 0, respectively, whichpoint just beyond the last QWORD that the controller 102 has written tothe corresponding priority receive status ring. The CSB 196 alsocomprises an interrupt zero register copy INT0_COPY, which is a copy ofthe contents of an interrupt 0 register in the controller 102.

FIG. 11C illustrates registers 132 related to the descriptor managementunit 130 in the controller 102. Transmit descriptor base pointersTX_RING[3:0]_BASE include the memory addresses of the start of thetransmit descriptor rings of corresponding priority, and the lengths ofthe transmit descriptor rings are provided in TX_RING[3:0]_LENregisters. Transmit descriptor write pointers are stored in registersTX_WR_PTR[3:0], where the driver software 190 updates these registers topoint just beyond the last QWORD that the driver has written to thecorresponding transmit descriptor ring. Receive descriptor base pointersRX_RING[3:0]_BASE include the memory address (e.g., in host memory 128)of the start of the receive descriptor rings of corresponding priority,and the lengths of these receive descriptor rings are provided inRX_RING[3:0]_LEN registers. Receive descriptor write pointersRX_WR_PTR[3:0] are updated by the driver 190 to point just beyond thelast QWORD that the driver has written to the corresponding receivedescriptor ring. Receive status ring base pointer registersSTAT_RING[3:0]_BASE indicate the memory address of the receive statusrings, and STAT_RING[3:0]_BASE indicate the lengths of the correspondingreceive status rings 199 in memory 128. RX_BUF_LEN indicates the numberof QWORDS of the receive data buffers 194, where all the receive databuffers 194 are of the same length, and CSB_ADDR indicates the addressof the CSB 196 in the host memory 128.

To further illustrate descriptor management operation in datatransmission, FIG. 11D illustrates the host memory 128 and thedescriptor management unit 130, including an exemplary transmitdescriptor ring in the host memory 128 and the corresponding descriptorregisters 132 in the descriptor management unit 130 of the controller102. In addition, FIGS. 11E and 11F illustrate an exemplary transmitdescriptor 192 a and control flags thereof, respectively. In thetransmit descriptor 102 of FIG. 11E, BUF1_ADR[39:0] includes an addressin the host memory 128 of the first data buffer 194 associated with thedescriptor 192 a. The descriptor 192 a also includes transmit flags(TFLAGS1, FIGS. 11E and 11F) 193, which include a MORE_CTRL bit toindicate inclusion of a second 64-bit control word with informationrelating to virtual local area network (VLAN) operation and TCPsegmentation operation. An ADD_FCS/IVLEN1 bit and an IVLEN0 bit are usedfor controlling FCS generation in the absence of IPsec processing, or toindicate the length of an encapsulation security protocol (ESP)initialization vector (IV) when IPsec security and layer 4 processingare selected. An IPCK bit is used to indicate whether the controller 102generates a layer 3 (IP layer) checksum for transmitted frames, and anL4CK flag bit indicates whether the controller 102 generates a layer 4(e.g., TCP, UDP, etc.) checksum. Three buffer count bits BUF_CNTindicate the number of data buffers 194 associated with the descriptor192 a, if less than 8. If more than 8 data buffers 194 are associatedwith the descriptor 192 a, the buffer count is provided in theBUF_CNT[7:0] field of the descriptor 192 a.

A BYTECOUNT1[15:0] field in the descriptor 192 a indicates the length ofthe first data buffer 194 in bytes. A PAD_LEN field includes a padlength value from an ESP trailer associated with the frame and a NXT_HDRfield provides next header information (protocol data for IPv4) from theESP trailer if the MORE_CTRL bit is set. Following the NXT_HDR field, anESP_AUTH bit 195 indicates whether the frame includes an authenticationdata field in the ESP trailer, and a security association (SA) pointerfield SA_PTR[14:0] points to an entry in the external SA memory 140(FIG. 9A) that corresponds to the frame. A two bit VLAN tag controlcommand field TCC[1:0] 197 includes a command which causes thecontroller 102 to add, modify, or delete a VLAN tag or to transmit theframe unaltered, and a maximum segment size field MSS[13:0] specifiesthe maximum segment size that the TCP segmentation hardware of thecontroller 102 will generate for the frame associated with thedescriptor 192 a. If the contents of the TCC field are 10 or 11, thecontroller 102 will transmit the contents of a tag control informationfield TCI[15:0] as bytes 15 and 16 of the outgoing frame. Where theframe data occupies more than one data buffer 194, one or moreadditional buffer address fields BUF_ADR[39:0] are used to indicate theaddresses thereof, and associated BYTECOUNT[15:0] fields are used toindicate the number of bytes in the extra frame buffers 194.

When the network software driver 190 writes a descriptor 192 to adescriptor ring, it also writes to a descriptor write pointer register132 in the descriptor management unit registers 132 to inform thecontroller 102 that new descriptors 192 are available. The value thatthe driver writes to a given descriptor management register 132 is apointer to a 64-bit word (QWORD) in the host memory 128 just past thedescriptor 192 that it has just written, wherein the pointer is anoffset from the beginning of the descriptor ring measured in QWORDs. Thecontroller 102 does not read from this offset or from anything beyondthis offset. When a transmit descriptor write pointer register (e.g.,DMU register 132, such as TX_WR_PTR1 in FIG. 11D) has been written, thecontroller 102 starts a transmission process if a transmission is notalready in progress. When the transmission process begins, it continuesuntil no unprocessed transmit descriptors 192 remain in the transmitdescriptor rings. When the controller 102 finishes a given transmitdescriptor 192, the controller 102 writes a descriptor read pointer(e.g., pointer TX_RD_PTR1 in FIG. 11D) to the CSB 196.

At this point, the descriptor read pointer TX_RD_PTR1 points to thebeginning of the descriptor 192 that the controller 102 will read next.The value of the descriptor 192 is the offset in QWORDs of the QWORDjust beyond the end of the last descriptor that has been read. Thispointer TX_RD_PTR1 thus indicates to the driver 190 which part ofdescriptor space it can reuse. The driver 190 does not write to thelocation in the descriptor space that the read pointer points to or toanything between that location and 1 QWORD before the location that thedescriptor write pointer TX_WR_PTR1 points to. When the descriptor readpointer TX_RD_PTR1 is equal to the corresponding descriptor writepointer TX_WR_PTR1, the descriptor ring is empty. To distinguish betweenthe ring empty and ring full conditions, the driver 190 insures thatthere is always at least one unused QWORD in the ring. In this manner,the transmit descriptor ring is full when the write pointer TX_WR_PTR1is one less than the read pointer TX_RD_PTR1 modulo the ring size.

Referring also to FIG. 11G, an exemplary receive descriptor 192 b isillustrated, comprising a pointer BUF_ADR[39:0] to a block of receivebuffers 194 in the host system memory 128, and a count fieldBUF_MULT[7:0] indicating the number of buffers 194 in the block, whereinall the receive buffers 194 are the same length and only one buffer isused for each received frame in the illustrated example. If the receivedframe is too big to fit in the buffer 104, the frame is truncated, and aTRUNC bit is set in the corresponding receive status ring entry 199.FIG. 11H illustrates an exemplary receive descriptor ring comprising aninteger number n receive descriptors 192 b for storing addressespointing to n receive data buffers 194 in the host memory 128. Theregisters 132 in the descriptor management unit 130 of the controller102 include ring base and length registers (RX_RING1_BASE andRX_RING1_LEN) corresponding to the receive descriptor ring, as well as areceive write pointer register (RX_WR_PTR1) including an address of thenext unused receive descriptor 192 b in the illustrated descriptor ring,and a receive buffer length register (RX_BUF_LEN) including the lengthof all the buffers 194. The descriptor management unit 130 also hasregisters 132 (STAT_RING1_BASE and STAT_RING1_LEN) related to thelocation of the receive status ring having entries 199 corresponding toreceived data within one or more of the buffers 194. The control statusblock 196 in the host memory 128 also includes a register STAT_WR_PTR1whose contents provide the address in the receive status ring of thenext unused status ring location, wherein the receive status ring isconsidered empty if STAT_WR_PTR1 equals RX_WR_PTR1.

FIGS. 11I and 11J illustrate further details of an exemplary receivestatus ring 199 and an entry therefor, respectively. The exemplaryreceive status ring entry of FIG. 11J includes VLAN tag controlinformation TCI[15:0] copied from the receive frame and a message countfield MCNT[15:0] indicating the number of bytes received which arecopied in the receive data buffer 194. A three bit IPSEC_STAT1[2:0]field indicates encoding status from the IPsec security system 124 and aTUNNEL_FOUND bit indicates that a second IP header was found in thereceived data frame. An AH_ERR bit indicates an authentication header(AH) failure, an ESPAH_ERR bit indicates an ESP authentication failure,and a PAD_ERR bit indicates an ESP padding error in the received frame.A CRC bit indicates an FCS or alignment error and a TRUNC bit indicatesthat the received frame was longer than the value of the RX_BUF_LENregister 132 (FIG. 11C above), and has been truncated. A VLAN tag typefield TT[1:0] indicates whether the received frame is untagged, prioritytagged, or VLAN tagged, and an RX_MATCH[2:0] field indicates a receiveaddress match type. An IP_CK_ERR bit indicates an IPv4 header checksumerror, and an IP header detection field IP_HEADER[1:0] indicates whetheran IP header is detected, and if so, what type (e.g., IPv4 or IPv6). AnL4_CK-ERR bit indicates a layer 4 (e.g., TCP or UDP) checksum error inthe received frame and a layer 4 header detection field L4_HEADERindicates the type of layer 4 header detected, if any. In addition, areceive alignment length field RCV_ALIGN_LEN[5:0] provides the length ofpadding inserted before the beginning of the MAC header for alignment.

As shown in FIGS. 11H and 111, in receive operation, the controller 102writes receive status ring write pointers STAT_WR_PTR[3:0] (FIG. 11B) tothe CSB 196. The network driver software 190 uses these write pointersto determine which receive buffers 194 in host memory 128 have beenfilled. The receive status rings 199 are used to transfer statusinformation about received frames, such as the number of bytes receivedand error information, wherein the exemplary system provides fourreceive status rings 199, one for each priority. When the controller 102receives an incoming frame from the network 108, the controller 102 usesthe next receive descriptor 192 from the appropriate receive descriptorring to determine where to store the frame in the host memory 128. Oncethe received frame has been copied to system memory 128, the controller102 writes receiver status information to the corresponding receivestatus ring 199. Synchronization between controller 102 and the driversoftware 190 is provided by the receive status write pointers(STAT_WR_PTR[3:0]) in the CSB 196. These pointers STAT_WR_PTR[3:0] areoffsets in QWORDs from the start of the corresponding ring.

When the controller 102 finishes receiving a frame from the network 108,it writes the status information to the next available location in theappropriate receive status ring 199, and updates the correspondingreceive status write pointer STAT_WR_PTR. The value that the controller102 writes to this location is a pointer to the status entry in the ringthat it will write to next. The software driver 190 does not read thisentry or any entry past this entry. The exemplary controller 102 doesnot have registers that point to the first unprocessed receive statusentry in each ring. Rather, this information is derived indirectly fromthe receive descriptor pointers RX_WR_PTR. Thus, when the softwaredriver 190 writes to one of the RX_WR_PTR registers 132 (FIG. 11C) inthe controller 102, the driver 190 ensures that enough space isavailable in the receive status ring 199 for the entry corresponding tothis buffer 104.

Transmit Data Frames

Referring now to FIGS. 9A-10 and 12A-12E, the controller 102 transmitsframes 200 from the data buffers 194 in host memory 128 using thetransmit descriptors 192 described above. When an application softwareprogram 184 running in the host processor 112 needs to send a packet ofdata or information to another computer or device on the network 108,the packet is provided to the operating system layer 4 and 3 software(e.g., TCP layer software 186 and IP software 188 in FIG. 10). Thesesoftware layers construct various headers and trailers to form atransmit frame 200. The network interface driver software 190 thenassembles the frame 200, including one or more headers and the datapacket, into the host memory data buffers 194 and updates thedescriptors and descriptor management unit registers 132 in thecontroller 102 accordingly. The assembled frame in the data buffers 194includes layer 3 and layer 4 headers and corresponding checksums (e.g.,IP and TCP headers and checksums), as well as a MAC header, asillustrated in FIGS. 13A and 13B. FIGS. 12A and 12C schematicallyillustrate the formation of transmit frames 200 a and 200 c using layer4 TCP and layer 3 interne protocol version 4 (IPv4) for transport andtunnel modes, respectively, and FIGS. 12B and 12D schematicallyillustrate the formation of transmit frames 200 b and 200 d using IPv6for transport and tunnel modes, respectively. However, the invention isnot limited to TCP/IP implementations, wherein other protocols may beused. For example, the exemplary controller 102 may also be used fortransmission and receipt of data using user data gram protocol (UDP)layer 4 software.

In FIGS. 12A-12D, the original data packet from the application software184 is provided to the TCP layer 186 as TCP data 202. The TCP layer 186stores the TCP data 202 in host memory 128 and creates a TCP header 204.The TCP Exemplary TCP headers are illustrated and described below withrespect to FIGS. 13A and 13B. The TCP data 202 and TCP header (e.g., orpointers thereto) are provided to the layer 3 software (e.g., IP layer188 in this example). The IP layer 188 creates an IP header 206 (e.g.,IPv4 headers 206 a in FIGS. 12A and 12C, or IPv6 headers 206 b in FIGS.12B and 12D). For IPv6 (FIGS. 12B and 12D), the IP layer 188 may alsocreate optional extension headers 208.

Where transmit security processing is to be employed, including ESPencryption and authentication, the IP layer 188 also creates an ESPheader 210, and ESP trailer 212, and an ESP authentication field 214 forIPv4 (FIGS. 12A and 12C). For IPv6 in transport mode (FIG. 12B), ahop-by-hop destination routing field 216 and a destination option field218 are created by the IP layer 188. For IPv4 in tunnel mode, the IPlayer 188 also creates a new IPv4 header 220. For IPv6 in tunnel mode(FIG. 12D), the IP layer 188 further creates a new IPv6 header 222 andnew extension headers 224 preceding the ESP header 210.

For the frame 200 a of FIG. 12A, the TCP header 204, the TCP data 202,and the ESP trailer 212 are encrypted, wherein the host software may dothe encryption or the exemplary network interface controller 102 may beconfigured to perform the encryption. Authentication is performed acrossthe ESP header 210 and the encrypted TCP header 204, the TCP data 202,and the ESP trailer 212. For the transport mode IPv6 frame 200 b in FIG.12B, the destination option 218, the TCP header 204, the TCP data 202,and the ESP trailer 212 are encrypted and the ESP header 210 isauthenticated together with the encrypted TCP header 204, the TCP data202, and the ESP trailer 212. In tunnel mode IPv4 example of FIG. 12C,the TCP header 204, the TCP data 202, the original IPv4 header 206 a,and the ESP trailer 212 are encrypted and may then be authenticatedalong with the ESP header 210. For the IPv6 tunnel mode example of FIG.12D, the TCP header 204, the TCP data 202, the ESP trailer 212, theoriginal extension headers 208, and the original IPv6 header 206 b areencrypted, with these and the ESP header 210 being authenticated.

FIG. 12E illustrates an exemplary transmit frame 200 a after creation ofthe ESP header 210 and trailer 212, showing further details of anexemplary ESP header 210. The ESP header 210 includes a securityparameters index (SPI), which, in combination with destination IPaddress of the IP header 206 a and the ESP security protocol uniquelyidentifies the security association (SA) for the frame 200 a. The ESPheader 210 further includes a sequence number field indicating a countervalue used by the sender and receiver to identify individual frames,where the sender and receiver counter values are initialized to zerowhen a security association is established. The payload data of theframe 200 a includes an initialization vector (IV) 226 if the encryptionalgorithm requires cryptographic synchronization data, as well as theTCP data 202 and TCP or other layer 4 header 204.

Padding bytes 230 are added as needed to fill the plain text data to bea multiple of the number of bytes of a cipher block for an encryptionalgorithm, and/or to right-align the subsequent PAD LENGTH and NEXTHEADER fields 232 and 234, respectively, in the ESP trailer 212 within a4-byte word, thereby ensuring that the ESP authentication data 214following the trailer 212 is aligned to a 4-byte boundary. In the ESPtrailer 212, the PAD LENGTH field 232 indicates the number of PAD bytes230, and the NEXT HEADER field 234 identifies the type of data in theprotected payload data, such as an extension header in IPv6, or an upperlayer protocol identifier (e.g., TCP, UDP, etc.). Where securityprocessing is selected for the frame 200 a, the IP layer 188 modifiesthe protocol header immediately preceding the ESP header 210 (e.g., theIPv4 header 206 a in the illustrated frame 200 a) to have a value (e.g.,‘50’) in the PROTOCOL field (e.g., ‘NEXT HEADER’ field for IPv6)indicating that the subsequent header 210 is an ESP header.

FIGS. 13A and 13B illustrate exemplary TCP frame formats 200 e and 200 ffor IPv4 and IPv6, respectively, to show the contents of variousheaders. In FIG. 13A, the exemplary frame 200 e is illustrated having aTCP data packet 202, a TCP header 204, an IPv4 header 206 a and a MACheader 240, as well as a 4-byte FCS field for a frame check sequence. InFIG. 13B, the frame 200 f similarly includes a TCP data packet 202, aTCP header 204, and a MAC header 240, as well as a 4-byte FCS field andan IPv6 header 206 b. In both cases, the TCP checksum is computed acrossthe TCP data 202 and the TCP header 204. In the IPv4 example 200 e, theIPv4 header checksum is computed across the IPv4 header 206 a (HEADERCHECKSUM field of the IPv4 header 206 a), the IP total length is acrossthe IPv4 header 206 a, the TCP header 204, and the TCP data 202 (TOTALLENGTH field in the IPv4 header 206 a), and the IEEE 802.3 length is theIP total length plus 0-8 bytes in the optional LLC & SNAP field of theMAC header 240 (802.3 LENGTH/TYPE field in the MAC header). In the IPv6example 2006 of FIG. 13B, the IEEE 802.3 length is the TCP data 202 plusthe TCP header 204 and any optional extension headers (illustrated asthe last field in the IPv6 header in FIG. 13B), the value of which goesinto the LENGTH/TYPE field of the MAC header 240, and the IP payloadlength is the TCP data 202 plus the TCP header 204 and any optionalextension headers (PAYLOAD LENGTH field of the IPv6 header 206 b).

TCP Segmentation

Referring now to FIGS. 14A-14D and 15, the controller 102 can optionallyperform outgoing TCP and/or IP layer checksumming, TCP segmentation,and/or IPsec security processing. Where one or more of these functionsare offloaded from the host processor 112 to the controller 102, thelayer 3 software 186 may provide certain of the fields in the frame 200(e.g., checksums, lengths, etc.) with pseudo values. With respect to TCPlayer segmentation, the controller 102 can be programmed toautomatically retrieve a transmit frame from the host memory 128, andwhere the frame is large, to break the large frame into smaller framesor frame segments which satisfy a maximum transmission unit (MTU)requirement of the network 108 using a TCP segmentation system 260. Thesegmentation system 260 comprises any circuitry operatively coupled withthe descriptor management unit 130, which is configured to perform thesegmentation tasks as described herein. The controller 102 thentransmits these segments with the appropriate MAC, IP, and TCP headers.In the illustrated example, the original TCP frame 200 in the hostsystem memory 128 is in the form of a (possibly oversized) IEEE 802.3 orEthernet frame complete with MAC, IP, and TCP headers. In the exemplarycontroller 102, the IP headers 206 can be either version 4 or version 6,and the IP and TCP headers may include option fields or extensionheaders. The network controller 102 will use suitably modified versionsof these headers in each segmented frame that it automaticallygenerates. In the exemplary device 102, the original TCP frame can bestored in host system memory 128 in any number of the buffers 194,wherein all headers from the beginning of the frame through the TCPheader 204 are stored in the first buffer 194.

Referring also to FIGS. 13A and 13B, the frame fields 802.3 LENGTH/TYPE,TOTAL LENGTH, IDENTIFICATION, HEADER CHECKSUM, SEQUENCE NUMBER, PSH,FIN, and TCP CHECKSUM fields of the IPv4 frame 200 e (FIG. 13A) aremodified in the controller 102 and the others are copied directly fromthe original frame. In FIG. 13B, the LENGTH/TYPE, PAYLOAD LENGTH,SEQUENCE NUMBER, PSH, FIN, and TCP CHECKSUM fields in the frame 200 fwill be modified in the controller 102 for each generated (e.g.,segmented) frame. To enable automatic TCP segmentation for a frame 200by the controller 102, the driver 190 in the host 112 sets the bits inthe MORE_CTRL field (FIG. 11F) of the corresponding transmit descriptor192, and also includes a valid value for the maximum segment size(MSS[13:0]) field of the descriptor 192. For all corresponding generatedframes except for the last frame, the length will be the value of theMSS[13:0] field plus the lengths of the MAC, IP, and TCP headers 240,206, and 204, respectively, plus four bytes for the FCS. The length ofthe last frame generated may be shorter, depending on the length of theoriginal unsegmented data.

FIG. 14A illustrates a table 250 showing frame fields modified byoutgoing ESP processing, and FIG. 14B shows a table 252 with the framefields modified by authentication header (AH) processing, wherein thetables 250 and 252 further indicate which frame fields are created bythe host processor software, and those added by the controller 102.Before submitting a transmit frame to the controller 102 for automaticTCP segmentation, the IP layer 188 provides an adjusted pseudo headerchecksum in the TCP checksum field of the TCP header 204. FIGS. 14C and14D provide tables 254 and 256 illustrating pseudo header checksumcalculations for IPv4 and IPv6, respectively, performed by the IF layersoftware 188 in generating the transmit frames 200. The value of thischecksum is a standard TCP pseudo header checksum described in theTransmission Control Protocol Functional Specification (RFC 793),section 3.1 for IPv4 frames and in the Internet Protocol, Version 6Specification (RFC 2460), section 8.1 for IPv6 frames, except that thevalue zero is used for the TCP length in the calculation. The controller102 adds the TCP length that is appropriate for each generated segment.

For IPv4 frames, the pseudo header 254 in FIG. 14C includes the 32-bitIP source address, the 32-bit IP destination address, a 16-bit wordconsisting of the 8-bit Protocol Field from the IP Header padded on theleft with zeros, and the TCP length (which is considered to be 0 in thiscase). For IPv6 frames, the pseudo header 256 in FIG. 14D includes the128-bit IPv6 source address, the 128-bit IPv6 destination address, the16-bit TCP length (which is considered to be zero), and a 16-bit wordconsisting of the 8-bit Protocol identifier padded on the left withzeros. The 8-bit protocol identifier is the contents of the Next Headerfield of the IPv6 Header or of the last IPv6 extension Header, ifextension headers are present, with a value of 6 for TCP. If TCP or UDPchecksum generation is enabled without TCP segmentation, the TCP lengthused in the pseudo header checksum includes the TCP header plus TCP datafields. However, when TCP segmentation is enabled, the controller 102automatically adjusts the pseudo header checksum to include the properlength for each generated frame.

Where the controller 102 is programmed to perform TCP segmentation, thevalues of the various modified fields are calculated as described below.The LENGTH/TYPE field in the MAC header 240 is interpreted as either alength or an Ethernet type, depending on whether or not its value isless than 600 h. If the value of the field is 600 h or greater, thefield is considered to be an Ethernet type, in which case the value isused for the LENGTH/TYPE field for all generated frames. However, if thevalue is less than 600 h, the field is interpreted as an IEEE 802.3length field, in which case an appropriate length value is computed inthe controller 102 for each generated frame. The value generated for thelength field will indicate the length in bytes of the LLC Data portionof the transmitted frame, including all bytes after the LENGTH/TYPEfield except for the FCS, and does not include any pad bytes that areadded to extend the frame to the minimum frame size. The Tx parser 162in the controller 102 parses the headers of the transmit frames 200 todetermine the IP version (IPv4 or IPv6) and the location of the variousheaders. The IPv4 TOTAL LENGTH is the length in bytes of the IPv4datagram, which includes the IPv4 header 206 a (FIG. 13A), the TCPheader 204, and the TCP data 202, not including the MAC header 240 orthe FCS. If the IP version is 4, the hardware will use this informationto generate the correct TOTAL LENGTH field for each generated frame. ForIPv6, the PAYLOAD LENGTH field is computed as the number of bytes of theframe 200 f between the first IPv6 header and the FCS, including anyIPv6 extension headers. For both IPv4 and IPv6, the Tx parser 162generates the corresponding TOTAL LENGTH or PAYLOAD LENGTH field valuesfor each generated transmit frame where TCP segmentation is enabled.

Because each generated TCP segment is transmitted as a separate IFframe, the IDENTIFICATION field in the IPv4 header of each segment frameis unique. In the first such segment frame, the IDENTIFICATION field iscopied from the input frame by the Tx parser 162 into the appropriatelocation in the first memory 116 in constructing the first segmentframe. The parser 162 generates IDENTIFICATION fields for subsequentsegment frames by incrementing by one the value used for the previousframe. For the SEQUENCE NUMBER field in the TCP header 204, the TCPprotocol software 186 establishes a logical connection between twonetwork nodes and treats all TCP user data sent through this connectionin one direction as a continuous stream of bytes, wherein each suchframe is assigned a sequence number. The TCP SEQUENCE NUMBER field ofthe first TCP packet includes the sequence number of the first byte inthe TCP data field 202. The SEQUENCE NUMBER field of the next TCP packetsent over this same logical connection is the sequence number of theprevious packet plus the length in bytes of the TCP data field 202 ofthe previous packet. When automatic TCP segmentation is enabled, the Txparser 162 of the controller 102 uses the TCP SEQUENCE NUMBER field fromthe original frame for the sequence number of the first segment frame200, and the SEQUENCE NUMBER for subsequent frames 200 is obtained byadding the length of the TCP data field 202 of the previous frame 200 tothe SEQUENCE NUMBER field value of the previous segment frame 200.

The TCP push (PSH) flag is an indication to the receiver that it shouldprocess the received frame immediately without waiting for thereceiver's input buffer to be filled, for instance, where the inputbuffer may have space for more than one received frame. When automaticTCP segmentation is requested, the parser 162 in the controller 102 setsthe PSH bit to 0 for all generated frames 200 except for the last frame200, which is set to the value of the PSH bit from the original inputframe as set by the TCP layer software 186. The TCP finish (FIN) flag isan indication to the receiver that the transmitter has no more data totransmit. When automatic TCP segmentation is requested, the parser 162sets the FIN bit to 0 for all generated segment frames 200 except forthe last frame 200. The parser 162 inserts the value of the FIN bit fromthe original input frame (e.g., from the TCP layer software 186) for thevalue of the FIN bit in the last generated segment frame 200.

Checksum Generation and Verification

The exemplary controller 102 may be programmed or configured to generatelayer 3 (e.g., IP) and/or layer 4 (e.g., TCP, UDP, etc.) checksums fortransmitted frames 200, and to automatically verify such checksums forincoming (e.g., received) frames 200. The exemplary controller 102accommodates IP checksums as defined in RFC 791 (Internet Protocol), TCPchecksums defined in RFC 793 (Transmission Control Protocol) for IPv4frames 200 e, UDP checksums as defined in RFC 768 (User DatagramProtocol) for IPv4 frames, as well as TCP and UDP checksums for IPv6frames 200 f as set forth in RFC 2460 (Internet Protocol, Version 6Specification). With respect to IP checksums, the value for the HEADERCHECKSUM field in the IPv4 header 206 a is computed in the transmitchecksum system 164 as a 16-bit one's complement of a one's complementsum of all of the data in the IP header 206 a treated as a series of16-bit words. Since the TOTAL LENGTH and IDENTIFICATION fields aredifferent for each generated segment frame 200 e, the transmit checksumsystem 164 calculates a HEADER CHECKSUM field value for each segmentframe that the controller 102 generates.

The transmit checksum system 164 may also compute TCP layer checksumsfor outgoing frames 200. The value for the TCP CHECKSUM field in the TCPheader 204 is computed as a 16-bit one's complement of a one'scomplement sum of the contents of the TCP header 204, the TCP data 202,and a pseudo header that contains information from the IP header. Theheaders and data field are treated as a sequence of 16-bit numbers.While computing the checksum, the checksum field itself is replaced withzeros. The checksum also covers a 96 bit pseudo header (FIG. 14C or 14D)conceptually prefixed to the TCP header. This pseudo header contains thesource address, the destination address, the protocol, and TCP length.If the TCP Data Field contains an odd number of bytes, the last byte ispadded on the right with zeros for the purpose of checksum calculation.(This pad byte is not transmitted). To generate the TCP checksum for asegment frame 200, the transmit checksum system 164 updates the TCPSEQUENCE NUMBER field and the PSH and FIN bits of the TCP header 204 andsets the TCP CHECKSUM field to the value of the TCP CHECKSUM field fromthe original input frame 200. In addition, the transmit checksum system164 initializes an internal 16-bit checksum accumulator with the lengthin bytes of the TCP header 204 plus the TCP data field 202, adds theone's complement sum of all of the 16-bit words that make up themodified TCP header 204 followed by the TCP data 202 for the segment tothe accumulator, and stores the one's complement of the result in theTCP CHECKSUM field of the segment frame 200.

The IPCK and L4CK bits in the transmit descriptor 192 a (FIG. 11F)control the automatic generation of checksums for transmitted frames 200in the controller 102. Setting the IPCK bit causes the IP HeaderChecksum to be generated and inserted into the proper position in theIPv4 frame 200 e of FIG. 13A. Similarly setting L4CK causes either a TCPCHECKSUM or a UDP checksum to be generated, depending on which type oflayer 4 header is found in the outgoing frame 200. Since an IPv6 header206 b (FIG. 13B) does not have a header checksum field, the IPCK bit inthe descriptor is ignored for IPv6 frames 200 f. If TCP or UDP checksumgeneration is required for an outgoing frame 200, the layer 4 software186 also puts the pseudo header checksum in the TCP or UDP checksumfield. The controller 102 then replaces this value with the checksumthat it calculates over the entire TCP or UDP segment, wherein thevalues of the generated TCP or UDP checksum differs when TCPsegmentation is enabled. For TCP segmentation, the value 0 is used forthe TCP TOTAL LENGTH in the pseudo header checksum calculation. For TCPor UDP checksum generation, the TCP TOTAL LENGTH value is the length ofthe TCP header 204 plus the length of the TCP data 202 as described inthe RFCs referenced above.

The controller 102 can also be configured or programmed by the host 112to verify checksums for received frames via the checksum and pad checksystem 156. When so enabled or when security (e.g., IPsec) processing isrequired, the controller 102 examines incoming (e.g., received) framesto identify IPv4, IPv6, TCP and UDP headers, and writes thecorresponding codes to the IP_HEADER and L4_HEADER fields of the receivestatus ring 199 (FIG. 11J) entry to indicate which layer 3 and/or layer4 headers it has recognized. When the device recognizes a header havinga checksum, the receive checksum and pad check system 156 calculates theappropriate checksum as described in RFC 791, RFC 793, RFC 768, or RFC2460 and compares the result with the checksum found in the receivedframe. If the checksums do not agree, the device sets the IP_CK_ERRand/or L4_CK_ERR bit in the corresponding receive status ring entry 199.

Referring now to FIGS. 18, 19A, and 19B, further details of transmitchecksum generation are illustrated and described. In FIG. 18, a portionof the controller 102 is illustrated with respect to generation of a TCPchecksum value 290 for an outgoing data frame 200 having an ESP securityheader 210. FIGS. 19A and 19B illustrate an exemplary transmit checksumprocessing method 300 which may be implemented in the network interfacecontroller 102. TCP checksum processing for outgoing data begins at 302in FIG. 19A, wherein the layer 3 header (e.g., IP header) is parsed at303 to determine the subsequent header type and a determination is madeat 304 as to whether a security header is present in the outgoing dataframe. As seen in FIG. 18, the exemplary frame 200 in the assembly RAM160 includes an IP header 206 followed by an ESP security header 210. Inthis situation, the IP header 206 will have a value of 50 in itsPROTOCOL (IPv4) or NEXT HEADER (IPv6) field, indicating that thesubsequent header 210 is an ESP security header. In the controller 102,the transmit checksum parser 162 parses the IP header 206 as it isconcurrently provided to the TX checksum system 164 and the first memory216, to ascertain the value of this field. If the IP headerPROTOCOL/NEXT HEADER field has a value of 50, the frame 200 includes asecurity header (YES at 304), and the method 300 proceeds to 306.Otherwise, the method proceeds to 340 in FIG. 19B, as discussed below.

At 306, the descriptor management unit 130 obtains a transmit descriptor192 a from the host driver 190 (e.g., via the host memory 106) andobtains transmit checksum information from the descriptor at 308. Inorder to compute a TCP checksum value 290 across the TCP checksum rangein the frame 200, the transmit parser 162 needs to determine beginningand end points 292 and 294, respectively, for the TCP checksum range(e.g., including the TCP header 204 and the TCP data packet 202). Thiscan be done using the checksum information provided in the transmitdescriptor 192 a, which includes the TFLAGS1, PAD_LEN, and NXT_HDRfields (FIGS. 11E and 11F). At 310, the L4CK bit of the TFLAGS1 field ischecked. If the value is 0 (NO at 310), the method 300 proceeds to 312,as this value indicates that TCP checksumming is not requested for thisframe 200. For example, the host system 180 may be responsible forcomputing layer 4 checksums, in which case, the TCP header 214 includesa proper checksum value prior to the frame 200 being sent to thecontroller 102 for transmission.

If the L4CK bit equals 1 (YES at 310), the method 300 proceeds to 313,where the transmit parser 162 determines the header type of the headerfollowing the security header by parsing. A determination is then madeat 314 as to whether the header following the security header is a layer4 header (e.g., TCP in this example). If not (NO at 314), the transmitparser 162 continues parsing through any intervening headers (e.g.,extension headers, such as shown in FIG. 12D) until a layer 4 header isfound. Once the layer 4 header is found, determinations are made at 316and 318 as to whether the layer 4 header type information from thedescriptor 192 a is TCP or UDP. In the illustrated example, if the nextheader information from the descriptor 192 a is neither TCP nor UDP (NOat both 316 and 318), the controller 102 assumes a discrepancy exists,and the method 300 proceeds to 312 (no layer four checksum value iscomputed). If the next header information from the descriptor 192 aindicates a UDP or TCP header follows the security header (YES at 316 or318), the method 300 proceeds to 320 and 322, where the layer 4 checksumcomputation begins and ends, respectively, according to the transmitchecksum information and the parsed layer 3 header information.

In particular, the next header information NXT_HDR from the transmitdescriptor 192 a is employed at 320 to determine the start point for thelayer 4 checksum computation, and the padlength PAD_LEN and the IVlength information from the descriptor 192 a are used at 322. The parser162 ascertains the location of the end of the TCP data field 202 bytaking the IP total length or payload length information from the parsedlayer 3 header (IPv4 or IPv6 in FIGS. 13A and 13B) and subtracting thesum of the lengths of the security header (parsed at 303) and any otherintervening headers (parsed at 315), and also subtracting the lengths ofthe ESP trailer 212 and the ESP authentication field 214. The ESPtrailer 212 includes the padding bytes 230 (FIG. 12E), the length ofwhich is known from the PAD_LEN information in the transmit descriptor192 a, and the length of the ESP authentication field 214 is known fromthe IVLEN1 and IVLEN0 bits in the TFLAGS1 portion 193 of the transmitdescriptor 192 a. The resulting value of this computation is the lengthof the TCP header 204 and the TCP data 202, which is used at 322 to endthe TCP checksum computation.

The transmit parser 162 controls the transmit checksum system 162 tobegin checksum computation according to the start and end points 292 and294, and the system 164 generates the checksum value 290 (e.g., a TCPchecksum value in this example) accordingly. Once the checksum valuecomputation is finished, the method 300 proceeds to 324, where thetransmit checksum system 164 inserts the checksum value 290 into theappropriate location in the first memory 116 (e.g., within the TCPheader 204), after which the layer 4 checksum operation ends at 326.Thereafter, any selected security processing is performed at 328 (e.g.,using the IPsec system 124), and the outgoing frame is transmitted tothe network 108 at 330. If no layer 4 checksum is performed, the method300 proceeds directly from 312 to 328 for any required securityprocessing before the frame is transmitted at 330.

Referring also to FIG. 19B, if no security header is present in theoutgoing data frame 200 (NO at 304), the method 300 proceeds to 340 inFIG. 19B, where a determination is made as to whether the L4CK bit fromthe transmit descriptor 192 a equals 1. If not (NO at 340), the method300 proceeds to 342 and no layer 4 checksum computation is undertakenfor the frame 200. If the L4CK bit equals 1 (YES at 340), determinationsare made at 346 and 348 as to whether the layer 4 header type is TCP orUDP. If the next header information from the IP header 206 is neitherTCP nor UDP (NO at both 346 and 348), the controller 102 assumes adiscrepancy exists, and the method 300 proceeds to 342 (no layer fourchecksum value is computed). If the next header information indicates aTCP or UDP header follows the IP header 206, (YES at 346 or 348), thechecksum value computation begins and ends at 350 and 352, respectively,according to the parsed information. Once the layer 4 checksumcomputation is finished at 352, the checksum value 290 is inserted intothe frame 200 in the memory 116, the transmit checksum operations arefinished at 356, and the IPsec system 124 passes the frame 200 to thesecond memory 118 (e.g., no security processing in this case). Themethod 300 then returns to 330 (FIG. 19A), and the frame 200 istransmitted to the network 108.

Security Processing

Referring now to FIGS. 9A-10, 15, 16, and 17A-17E, the exemplary IPsecsecurity system 124 is configurable to provide internet protocolsecurity (IPsec) authentication and/or encryption/decryption servicesfor transmitted and received frames 200 in accordance with RFC 2401. Forauthentication header (AH) processing the module implements theHMAC-MD5-96 algorithm defined in RFC 2404 and the HMAC-SHA-1-96 definedin RFC 2404. The HMAC-MD5-96 implementation provides a 128-bit key, a512-bit block size, and a 128-bit message authentication code (MAC),truncated to 96 bits. The implementation of the HMAC-SHA-1-96 algorithmprovides a n 160-bit key, a 512-bit block size, and a 160-bit messageauthentication code (MAC), truncated to 96 bits. For encapsulatingsecurity payload (ESP) processing, the IPsec module 124 also implementsthe HMAC-MD5-96 and HMAC-SHA-1-96 algorithms for authentication and theESP DES-CBC (RFC 2406), the 3DES-CBC, and the AES-CBC(draft-ietf-ipsec-ciph-aes-cbc-01) encryption algorithms. The DES-CBCalgorithm in the IPsec module 124 provides a 64-bit key (including 8parity bits), a 64-bit block size, and cipher block chaining (CBC) withexplicit initialization vector (IV). The 3DES-CBC algorithm provides a192-bit key (including 24 parity bits), a 64-bit block size, and CBCwith explicit IV. The AES-CBC algorithm provides a 128-, 192-, or256-bit key; 10, 12, or 14 rounds, depending on key size; a 128-bitblock size, and CBC with explicit IV.

The exemplary security system 124 provides cryptographically-based IPsecsecurity services for IPv4 and IPv6, including access control,connectionless integrity, data origin authentication, protection againstreplays (a form of partial sequence integrity), confidentiality(encryption), and limited traffic flow confidentiality. These servicesare provided at layer 3 (IP layer), thereby offering protection for IPand/or upper layer protocols through the use of two traffic securityprotocols, the authentication header (AH) and the encapsulating securitypayload (ESP), and through the use of cryptographic key managementprocedures and protocols. The IP authentication header (AH) providesconnectionless integrity, data origin authentication, and an optionalanti-replay service, and the ESP protocol provides confidentiality(encryption), and limited traffic flow confidentiality, and may provideconnectionless integrity, data origin authentication, and an anti-replayservice. The AH and ESP security features may be applied alone or incombination to provide a desired set of security services in IPv4 andIPv6, wherein both protocols support transport mode and tunnel mode. Intransport mode, the protocols provide protection primarily for upperlayer protocols and in tunnel mode, the protocols are applied totunneled IP packets.

For outgoing frames 200, the controller 102 selectively provides IPsecauthentication and/or encryption processing according to securityassociations (SAs) stored in the SA memory 140. If an outgoing frame 200requires IPsec authentication, the IPsec unit 124 calculates anintegrity check value (ICV) and inserts the ICV into the AH header orESP trailer 212 (FIGS. 12A-12D). If the frame 200 requires encryption,the unit 124 replaces the plaintext payload with an encrypted version.For incoming (e.g., received) frames, the IPsec unit 124 parses IPsecheaders to determine what processing needs to be done. If an IPsecheader is found, the IPsec system 124 uses the security parameters index(SPI) from the header plus the IPsec protocol type and IP destinationaddress to search the SA memory 140 to retrieve a security associationcorresponding to the received frame. Acceptable combinations of IPsecheaders for the exemplary controller 102 include an AH header, an ESPheader, and an AH header followed by an ESP header.

For IPsec key exchange, the host 112 negotiates SAs with remote stationsand writes SA data to the SA memory 140. In addition, the host 112maintains an IPsec security policy database (SPD) in the system memory128. For each transmitted frame 200 the host processor 112 checks theSPD to determine what security processing is needed, and passes thisinformation to the controller 102 in the transmit descriptor 192 a (FIG.11E) as a pointer SA_PTR[14:0] to the appropriate SA in the SA memory140. For incoming received frames 200 the controller 102 reports whatsecurity processing it has done in the receive status ring entry 199(FIG. 11J), and the host processor 112 checks the SPD to verify that theframe 200 conforms with the negotiated policy. The SAs includeinformation describing the type of security processing that must be doneand the encryption keys to be used. Individual security associationsdescribe a one-way connection between two network entities, wherein abi-directional connection requires two SAs for incoming and outgoingtraffic. SAs for incoming traffic are stored partly in an internal SPItable or memory 270 (FIG. 16) and partly in the external SA memory 140.These SA tables are maintained by the host processor 112, which writesindirectly to the SPI table 270 and the SA memory 140 by first writingto an SA data buffer in host memory 128 and then writing a command tothe SA address register. This causes the controller 102 to copy the datato the external SA memory 140 and to the internal SPI table memory 270.

One of the fields in an SPI table entry is a hash code calculated by thehost 112 according to the IP destination address. In addition, the host112 calculates a hash code based on the SPI to determine where to writean SPI table. If an incoming or outgoing SA requires authentication, thehost CPU calculates the values H(K XOR ipad) and H(K XOR opad) asdefined in RFC 2104, HMAC: Keyed-Hashing for Message Authentication,where the host 112 stores the two resulting 128 or 160-bit values in theSA memory 140. If necessary, at initialization time the host CPU canindirectly initialize the Initialization Vector (IV) registers used forCipher Block Chaining in each of four encryption engines in the IPsecsystem 124.

Referring to FIGS. 9A and 15, to begin a transmission process, the hostprocessor 112 prepares a transmit frame 200 in one or more data buffers194 in the host memory 128, writes a transmit descriptor 192 a (e.g.,FIG. 11E) in one of the transmit descriptor rings, and updates thecorresponding transmit descriptor write pointer (TX_WR_PTR[x]). Theframe data in the data buffers 194 includes space in the IPsec headersfor authentication data 214, for an initialization vector (IV) 226, andfor an ESP trailer 212 if appropriate (e.g., FIG. 12E). The contents ofthese fields will be generated by the IPsec system 124 in the controller102. Similarly, if padding is required (e.g., for alignment or to makethe ESP payload an integer multiple of encryption blocks), the paddingis included in the host memory buffers 194, and sequence numbers for theAH and ESP SEQUENCE NUMBER fields are provided in the data buffers 194by the host 112. The IPsec system 124 does not modify these fieldsunless automatic TCP segmentation is also selected, in which case theIPsec system 124 uses the sequence numbers from the buffers 194 for thefirst generated frame 200 and then increments these numbersappropriately for the rest of the generated segment frames. If IPsecprocessing is required for a particular outgoing frame 200, thecorresponding transmit descriptor 192 a includes a pointer in the SA_PTRfield to the appropriate SA entry in the external SA memory 140, and theIPsec system 124 uses information from the SA to determine how toprocess the frame 200. The transmit parser 162 examines the frame 200 todetermine the starting and ending points for authentication and/orencryption and where to insert the authentication data 214, ifnecessary.

If ESP encryption is required, the IPsec system 124 encrypts the payloaddata using the algorithm and key specified in the SA. If ESPauthentication is required, the system 124 uses the authenticationalgorithm and IPAD/OPAD information specified in the SA to calculate theauthentication data integrity check value (ICV), and stores the resultsin the authentication data field 214. If both ESP encryption andauthentication are required, the encryption is done first, and theencrypted payload data is then used in the authentication calculations.The encryption and authentication processes are pipelined so that theencryption engine within one of the IPsec processors 174 is processingone block of data while the authentication engine is processing theprevious block. The IPsec system 124 does not append padding to thepayload data field, unless automatic TCP segmentation is also enabled.The host processor 112 provides the ESP trailer 212 with appropriatepadding in the frame data buffers 194 in the system memory 128, and alsoprovides the proper value for the ESP SEQUENCE NUMBER field in the ESPheader 210 (FIG. 12E).

If ESP processing is combined with automatic TCP segmentation, the IPsecsystem 124 adds any necessary pad bytes to make the encrypted datalength a multiple of the block length specified for the selectedencryption algorithm. If ESP processing is combined with TCP or UDPchecksum generation, the host 112 provides correct NEXT HEADER and PADLENGTH values for the ESP trailer 212 and the Transmit Descriptor 192 a(FIG. 11E). If ESP processing is combined with automatic TCPsegmentation, the host 112 provides values for the NEXT HEADER and PADLENGTH fields of the transmit descriptor 192 a that are consistent withthe corresponding frame data buffers 194. In this combination, thecontroller 102 copies the NEXT HEADER field from the transmit descriptor192 a into the ESP trailer 212 of each generated frame 200, and uses thePAD LENGTH field of the descriptor 192 a to find the end of the TCP datafield 202 in the frame data buffer 194. In addition, the maximum segmentsize field MSS[13:0] of the transmit descriptor 192 a is decreased tocompensate for the IPsec header(s), the ESP padding, and the ICV.

Where ESP processing is combined with TCP segmentation or with TCP orUDP checksum generation, the software driver 190 sets the ESP_AH,IVLEN0, and IVLEN1 bits of the transmit descriptor 192 a accordingly.The transmit parser 162 uses this information to locate the TCP or UDPheader 204, and if no TCP or UDP processing is required, these bits areignored. For frames 200 requiring ESP processing, FIG. 14A illustrateswhich fields are created by the host 112 and included in the buffers 194and those fields that are modified by the ESP processing hardware in thesecurity system 124.

The encryption algorithms supported by the IPsec system 124 employcipher block chaining (CBC) mode with explicit initialization vectors(IVs 226, FIG. 12E). To allow a certain amount of parallel processingthe IPsec system 124 includes two TX IPSEC processor systems 174 a and174 b, each of which comprises a DES/3DES (data encryption standard)encryption system and an advanced encryption standard (AES) encryptionengine. Each of the four encryption engines in the TX IPSEC processors174 includes an N register, which are cleared to zero on reset. When thecontroller 102 is enabled, the contents of the N register associatedwith an encryption engine are used as the initialization vector 226 forthe first transmit frame 200 encrypted by that engine. Thereafter thelast encrypted data block from one frame 200 is used as the IV 226 forthe following frame 200. The host processor 112 can initialize the IVregisters in the IPsec system 124 with random data, for example, bytransmitting frames 200 with random data in the payload fields. In oneexample, the host 112 can put the external PHY device into an isolatemode to prevent these random data frames 200 from reaching the network108. The IPsec system 124 inserts the IV value 226 at the beginning ofthe payload field. The host 112 provides space in the frame data buffer194 for this field 226. The length of the IV 226 is the same as theencryption block size employed in the TX IPSEC processors 174, forexample, 64 bits for the DES and 3DES algorithms, and 128 bits for theAES algorithm.

Where authentication header (AH) processing is selected, the securitysystem 124 employs authentication algorithm and authentication ipad andopad data specified in the SA to calculate the authentication dataintegrity check value (ICV), and it stores the results in theauthentication data field 214. The transmit IPsec parser 170 detectsmutable fields (as defined by the AH specification, RFC 2402) andinsures that the contents of these fields and the authentication datafield 214 are treated as zero for the purpose of calculating the ICV. Inthe ICV calculation the IPsec system 124 employs the destination addressfrom the SA rather than the destination address from the packet's IPheader 206, to ensure that if source routing options or extensions arepresent, the address of the final destination is used in thecalculation. For transmit frames 200 that require AH processing, FIG.14B illustrates the fields created by the host 112 and included in thebuffers 194, as well as those fields modified by the AH processinghardware in the IPsec system 124.

Referring now to FIGS. 9A and 16, the IPsec system 124 provides securityprocessing for incoming (e.g., received) frames 200 from the network108. The RX parser 144 examines incoming frames 200 to find IPsecheaders, and looks up the corresponding SA in the SA memory 140. The RXIPSEC processor 150 then performs the required IPsec authenticationand/or decryption according to the SA. If decryption is required, theprocessor 150 replaces the original ciphertext in the frame 200 withplaintext in the memory 116. The descriptor management unit 130 setsstatus bits in the corresponding receive status ring entry 199 (FIG.11J) to indicate what processing was done and any errors that wereencountered.

FIG. 16 illustrates the flow of incoming data through the IPsec system124. The receive parser 144 examines the headers of incoming frames 200from the MAC engine 122 while the incoming frame 200 is being receivedfrom the network 108. The parser 144 passes the results of its analysisto the SA lookup logic 146. This information is also provided to thememory 118 in the form of a control block that is inserted betweenframes 200. The control block includes information about the types andlocations of headers in the incoming frame 200. If the parser 144 findsthat a frame 200 includes an IP packet fragment, IPsec processing isbypassed, and the frame 200 is passed on to the host memory 128 with theIP Fragment bit being set in the IPSEC_STAT1 field in the correspondingreceive status ring entry 199. For IPv4 frames, a fragment is identifiedby a non-zero fragment offset field or a non-zero more fragments bit inthe IPv4 header. For IPv6 packets, a fragment is indicated by thepresence of a fragment extension header.

If the parser 144 finds an IPsec header or an acceptable combination ofheaders, it passes the SPI, the IP destination address, and a bitindicating the IPsec protocol (AH or ESP) to the SA lookup engine 146.The SA lookup engine 146 uses the SPI, protocol bit, and a hash of thedestination address to search an internal SPI memory 270 (FIG. 16). Theresults of this search are written to the SA pointer FIFO 148, includinga pointer to an entry in the external SA memory 140, a bit thatindicates whether IPsec processing is required, and two bits thatindicate the success or failure of the SA lookup. The SA pointer FIFO148 includes an entry corresponding to each incoming frame 200 in thememory 118. If the SA pointer FIFO 148 does not have room for a newentry at the time that an incoming frame 200 arrives from the network108 or if the received frame 200 would cause the receive portion of thememory 118 to overflow, the frame 200 is dropped, and a receive missedpackets counter (not shown) is incremented.

An RX KEY FETCH state machine 262 (FIG. 16) retrieves the correspondingentry from the SA pointer FIFO 148 and determines what, if any,processing is required. If the control bits indicate that processing isrequired, the state machine 262 uses the contents of the pointer fieldto fetch the SA information from the external SA memory 140. If a DAfield of the SA does not match the DA field of the IP header in theframe 200, the IPsec processor 150 causes an error code to be written tothe receive status ring 199 and passes the frame 200 to the memory 118unmodified. If the DA field of the SA matches the DA field of the IPheader, the processor 150 decrypts the payload portion of the receivedframe 200 and/or checks the authentication data as required by the SA.

Referring also to FIGS. 17A-17D, the security association system used inoutgoing IPsec processing in the exemplary controller 102 is hereinafterdescribed. FIG. 17A illustrates an exemplary security association tablewrite access, FIG. 17B illustrates an exemplary SA address registerformat, FIG. 17C illustrates an exemplary SPI table entry in the SPImemory 270, and FIG. 17D illustrates an exemplary SA memory entry in theSA memory 140. The SA lookup engine 146 uses the SPI memory 270 and theexternal SA memory 140, both of which are maintained by the hostprocessor 112, where the exemplary SPI memory 270 is organized as acollection of 4096 bins, each bin having up to 4 entries. The address ofan entry in the SPI memory 270 is 14 bits long, with the 12 high orderbits thereof indicating a bin number. As illustrated in FIG. 17C, eachSPI table entry 272 in the SPI memory 270 includes a 32-bit securityparameters index SPI[31:0], a hash of the destination address DAHASH[39:32], a protocol bit PROTO indicating the security protocol(e.g., AH or ESP), and a VALID bit indicating whether the entry is validor unused.

FIG. 17D illustrates an exemplary entry 274 in the SA memory 140,wherein the SA memory 140 includes an entry corresponding to each entry272 in the SPI memory 270, with entries 274 and 272 in the two memories140 and 270 being in the same order. The entry 274 includes a three bitESP encryption algorithm field ESP_ALG indicating whether ESP encryptionis required, and if so, which algorithm is to be employed (e.g., DES;3DES; AES-128, 10 rounds; AES-192, 12 rounds; AES-256, 14 rounds; etc.).An electronic codebook bit ECB indicates whether ECB mode is used forencryption, and a two bit ESP authentication field ESPAH_ALG indicateswhether ESP authentication is required, and if so, which algorithm is tobe employed (e.g., MD5, SHA-1, etc.). A two bit AH field AH_ALGindicates whether AH processing is required, and if so which algorithmis to be employed (e.g., MD5, SHA-1, etc.). A protocol bit PROTOCOLindicates whether the first IPsec header is an ESP header or an AHheader, and an IPv6 bit indicates whether the SA is defined for IPv4 orIPv6 frames.

A BUNDLE bit indicates a bundle of two SAs specifying AH followed byESP, and a 32 bit SPI field specifies an SPI associated with the secondSA (e.g., ESP) in a bundle of 2 SAs, which is ignored for SAs that arenot part of bundles. An IP destination address field IPDA[127:0]indicates the address to which the SA is applicable, wherein the SAapplies only to packets that contain this destination address. AnAH_IPAD field includes a value obtained by applying the appropriateauthentication hash function (e.g., MD5 or SHA-1) to the exclusive OR ofthe AH authentication key and the HMAC ipad string as described in RFC2104. If the authentication function is MD5, the result is 16 bytes,which are stored in consecutive bytes starting at offset 24. If theauthentication function is SHA-1, the result is 20 bytes, which occupiesthe entire AH_TAD field. An AH_OPAD field includes a value obtained byapplying the appropriate authentication hash function (e.g., MD5 orSHA-1) to the exclusive OR of the AH authentication key and the HMACopad string as described in RFC 2104. If the authentication function isMD5, the result is 16 bytes, which are stored in consecutive bytesstarting at offset 44. If the authentication function is SHA-1, theresult is 20 bytes, which occupies the entire AH_OPAD field. The SAmemory entry 274 also includes an ESP_IPAD field having a value obtainedby applying the authentication hash function (MD5 or SHA-1) to theexclusive OR of the ESP authentication key and the HMAC ipad string asdescribed in RFC 2104, as well as an ESP_OPAD field including a valueobtained by applying the authentication hash function (MD5 or SHA-1) tothe exclusive OR of the ESP authentication key and the HMAC opad stringas described in RFC 2104. An encryption key field ENC_KEY includes anencryption/decryption key used for ESP processing.

The IPsec system 124 reads from the SA and SPI memories 140 and 270,respectively, but does not write to them. To minimize the lookup timethe SPI memory 270 is organized as a hash table in which the bin numberof an entry 272 is determined by a hash function of the SPI. The lookuplogic 146 uses the SPI and the IPsec protocol (AH or ESP) to search theSPI memory 270, by computing a hash value based on the SPI and using theresult to address a bin in the SPI memory 270. A second hash value iscomputed for the IP destination address, and the lookup logic 146compares the SPI, protocol, and destination address hash with entries inthe selected bin until it either finds a match or runs out of binentries. The lookup logic 146 then writes an entry into the SA pointerFIFO 148, including the address of the matching entry in the SPI memory270 and an internal status code that indicates whether or not IPsecprocessing is required and whether or not the SA lookup was successful.The Rx key fetch logic 262 fetches the DA from the SA memory 140 tocompare with the DA in the IP packet header. If the DA from the SAmemory 140 does not match the DA from the received frame 200, the frame200 is passed on to host memory 128 via the memory 116 and the businterface 106 without IPsec processing, and the corresponding receivestatus ring entry 199 indicates that no IPsec processing was done.

Referring also to FIG. 17A, the SA memory 140 and the SPI memory 270 aremaintained by the host processor 112. During normal operation, the host112 uses write and delete accesses to add and remove table entries 274,272. The exemplary SA memory 140 is divided into two regions, one forincoming SAs and one for outgoing SAs, wherein each region providesspace for 16K entries. Access to the SA and SPI memories 140 and 270 bythe host 112 is performed using an SA address register SA_ADDR 280 and a144-byte SA buffer 282. The SA buffer 282 holds one 136-byte SA memoryentry 274 followed by a corresponding 8-byte SPI table entry 272. Foroutgoing SAs, the SPI table entry section 272 of the buffer 282 is notused. To write an SA table entry, the host 112 creates a 136 or 144 byteentry in the host memory 128 and writes the target address in the SAmemory 140 to the SA_ADDR register 280. The controller 102 uses DMA tocopy the SA information first to the internal SA Buffer 282 and then tothe appropriate locations in the SA memory 140 and the SPI memory 270.The host 112 writes the physical address of an SA entry buffer 284 inthe host memory 128 to an SA_DMA_ADDR register 286. If the softwaredriver 190 uses the same buffer 284 in host memory 128 for loading allSA table entries, it only has to write to the SA_DMA_ADDR register 286once.

Incoming security associations are stored in locations determined by thehash algorithm. For outgoing (transmit) frames 200 the driver software190 includes a pointer to the appropriate SA in the transmit descriptor192 a (e.g., SA_PTR field in FIG. 11E). This makes it unnecessary forthe controller 102 to search the SA memory 140 for outgoing SAs, andtransmit SAs can be stored in any order. No outgoing SA is stored atoffset 0, since the value 0 in the SA_PTR field of the descriptor 192 ais used to indicate that no IPsec processing is required.

Referring also to FIG. 17B, the SA address register 280 includes theaddress of the SA table entries 274 to be accessed plus six SA accesscommand bits. These command bits include SA read, write, delete, andclear bits (SA_RD, SA_WR, SA_DEL, and SA_CLEAR), an SA direction bitSA_DIR, and a command active bit SA_ACTIVE. The read-only SA_ACTIVE bitis 1 while the internal state machine 262 is copying data to or from theSA buffer 282, during which time the host 112 refrains from accessingthe SA buffer 282. Selection between the incoming and outgoing regionsof the external SA memory 140 is controlled by the SA_DIR bit, whichacts as a high-order address bit. This bit is set to 1 for an incomingSA or to 0 for an outgoing SA. If this bit is set to 1, data istransferred to or from the internal SPI memory 270 as well as to or fromthe external SA memory 140. Outgoing SA table accesses affect only theexternal SA memory 140. When the host 112 sets the SA_RD in the SAaddress register 280, a state machine copies data from the external SAmemory 140 to the SA buffer 282. If the direction bit SA_DIR is 1, thecorresponding entry 272 from the internal SPI memory 270 is also copiedto the SA buffer 282. An SA address field SA_ADR[13:0] of the SA addressregister 280 points to the entries 272 and/or 274 to be copied.

When the host 112 sets the SA_WR bit in the SA_ADDR register 280, theresulting action depends on the value of the SA_DIR bit. If this bit is1 (e.g., indicating an incoming SA), the state machine copies data firstfrom the buffer 284 in host memory 128 into the internal SA buffer 282,and them from the SA buffer 282 into the external SA memory 140 and alsointo the corresponding internal SPI memory 270. If the SA_DIR bit is 0(e.g., indicating a transmit SA), when the access command is ‘write’,only the SA field of the SA buffer 282 is copied to the SA memory 140entry selected by the SA address register 280, and the SPI field is notcopied. For bundle processing, a BUNDLE bit is set in the SAcorresponding to the first IPsec header in the frame 200, indicatingthat the frame 200 is expected to include an AH header followed by anESP header. The corresponding entry in the external SA memory 140includes information for both these headers, including the expected SPIof the second IPsec header.

For receive AH processing, the value of the AH_ALG field in the SAmemory entry 274 is non-zero, indicating that AH processing is requiredfor the received frame 200. The Rx parser 144 scans the frame IP header(e.g., and IPv6 extension headers if present) to determine the locationsof mutable fields, as set forth in RFC 2402). The parser 144 inserts alist of these mutable field locations into the control block in thememory 118. If AH processing is enabled, the IPsec processor 150replaces the mutable fields and the ICV field of the AH header withzeros for the purpose of calculating the expected ICV (the frame datathat is copied to the host memory 128 is not altered). The destinationaddress field of the IP header is considered to be mutable butpredictable, because intermediate routers may change this field ifsource routing is used. However, since the originating node uses thefinal destination address for the ICV calculation, the receiver treatsthis field as immutable for its ICV check.

The control block in the memory 118 includes pointers to the startingand ending points of the portion of the received frame 200 that iscovered by AH authentication. The IPsec processor 150 uses this controlblock information to determine where to start and stop itsauthentication calculations. The AH_ALG field in the SA memory entry 274v indicates which authentication algorithm is to be used. The exemplaryIPsec system 124 provides HMAC-SHA-1-96 as defined in RFC 2404 andHMAC-MD5-96 as defined in RFC 2403 for AH processing. In either case theRx IPsec processor 150 uses preprocessed data from the AH_IPAD andAH_OPAD fields of the SA entry 274 along with the frame data to executethe HMAC keyed hashing algorithm as described in RFC 2104. If theresults of this calculation do not match the contents of theauthentication data field of the AH header, the AH_ERR bit is set in thecorresponding receive status ring entry 199 (FIG. 11J).

For receive ESP processing, the ESPAH_ALG field of the SA memory entry274 is non-zero, indicating that ESP authentication is required, and thenon-zero value indicates which authentication algorithm will be employed(e.g., MD5, SHA-1, etc.). The Rx IPsec processor 150 uses thepreprocessed ipad and opad data from the ESP_IPAD and ESP_OPAD fields ofthe SA entry 274 along with frame data to execute the HMAC keyed hashingalgorithm as described in RFC 2104. It uses pointers extracted from thecontrol block of the memory 118 to determine what part of the frame touse in the ICV calculation. The data used in the calculation start atthe beginning of the ESP header and ends just before the authenticationdata field of the ESP trailer, wherein none of the fields in this rangeare mutable. If the results of this ICV calculation do not match thecontents of the authentication data field in the ESP trailer, theESP_ICV_ERR bit is set in the corresponding receive status ring entry199.

If the ESP_ALG field of the SA memory entry 274 is non-zero, ESPdecryption is required, and the receive IPsec processor 150 uses theESP_ALG and ECB fields of the entry 274 to determine which decryptionalgorithm and mode to use (e.g., DES; 3DES; AES-128, 10 rounds; AES-192,12 rounds; AES-256, 14 rounds; etc.). The Rx IPsec processor 150retrieves the decryption key from the ENC_KEY field of the entry 274,and uses information from the control block in the memory 118 todetermine which part of the frame is encrypted (e.g., the portionstarting just after the ESP header and ending just before theauthentication data field of the ESP trailer). If the SA indicates thatno ESP authentication is to be performed, the length of theauthentication data field is zero and the encrypted data ends justbefore the FCS field.

Once the payload has been decrypted, the IPsec processor 150 checks thepad length field of the ESP trailer to see if pad bytes are present. Ifthe pad length field is non-zero, the processor 150 examines the padbytes and sets the PAD_ERR bit in the receive status ring entry 199 ifthe pad bytes do not consist of an incrementing series of integersstarting with 1 (e.g., 1, 2, 3, . . . ). The IPsec processor 150replaces the encrypted frame data with (decrypted) plaintext in thememory 118. The exemplary processor 150 does not reconstruct theoriginal IP packet (e.g., the processor 150 does not remove the ESPheader and trailer and replace the Next Header field of the previousunencrypted header). If the encryption uses CBC mode, the first 8 or 16bytes of the ESP payload field contain the unencrypted IV, which theIPsec processor 150 does not change. The encrypted data following the IVis replaced by its decrypted counterpart.

In the exemplary IPsec system 124, the SPI table bin number and the IPdestination address hash codes are both calculated using a single 12-bithash algorithm. The bin number is calculated by shifting the SPI throughhash logic in the IPsec processor 150. For the destination address (DA)hash, the 32-bit IPv4 destination address or the 128-bit IPv6destination address is shifted through the hashing logic, which provides12 output bits used for the bin number, where only the 8 leastsignificant bits are used for the DA hash. The hash function is definedby a programmable 12-bit polynomial in a configuration register of thecontroller 102, wherein each bit in the polynomial defines an AND/XORtap in the hash logic of the processor 150. The incoming bit stream isexclusive-ORed with the output of the last flip-flop in the hashfunction. The result is ANDed bitwise with the polynomial,exclusive-ORed with the output of the previous register, and thenshifted. The hash function bits are initialized with zeros. The searchkey is then passed through the hash function. After the input bit streamhas been shifted into the hash function logic, the 12-bit output is thehash key.

Although the invention has been shown and described with respect to acertain aspect or various aspects, it is obvious that equivalentalterations and modifications will occur to others skilled in the artupon the reading and understanding of this specification and the annexeddrawings. In particular regard to the various functions performed by theabove described components (assemblies, devices, circuits, etc.), theterms (including a reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (i.e., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary embodiments of theinvention. In addition, while a particular feature of the invention mayhave been disclosed with respect to only one of several aspects of theinvention, such feature may be combined with one or more other featuresof the other aspects as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the term“includes” is used in either the detailed description or the claims,such term is intended to be inclusive in a manner similar to the term“comprising.”

1. A method for partial coalescing transmit buffers comprising:receiving an array of virtual buffers for a data packet; mapping buffersof the array of virtual buffers to an array of physical buffers, whereinone or more of the physical buffers are associated with each of thevirtual buffers; analyzing the array of virtual buffers and the array ofphysical buffers for individual buffer sizes; on the array of virtualbuffers having a size greater than the array of associated physicalbuffers, selectively coalescing an initial number of buffers of thearray of virtual buffers into a coalesced buffer; and on the array ofvirtual buffers not having a size greater than the array of associatedphysical buffers, selectively coalescing an initial number of buffers ofthe array of physical buffers into the coalesced buffer.
 2. The methodof claim 1, further comprising forming a coalesced array from thecoalesced buffer and non-coalesced buffers of the array of physicalbuffers.
 3. The method of claim 2, further comprising passing thecoalesced array to a network device for transmission.
 4. The method ofclaim 1, wherein the initial number of selected buffers to coalescedepends on an initial fragment size.
 5. The method of claim 1, whereinthe coalesced buffer has a physical memory size and a physical address.6. The method of claim 1, wherein the array of virtual buffers isreceived from host software.
 7. A method for partial coalescing transmitbuffers comprising: obtaining a data packet from host software, whereinthe data packet is located in an array of virtual buffers that each mapto one or more physical buffers in a system memory; analyzing thevirtual buffers and the physical buffers associated with the datapacket; selectively copying either selected ones of the virtual buffersor selected ones of the physical buffers into a coalesced physicalbuffer based on the analysis; and wherein analyzing the virtual buffersand the physical buffers comprises: coalescing a determined number ofvirtual buffers into the single physical coalesced buffer if the totalsize of the virtual buffers is greater than the total size of thephysical buffers; and coalescing a determined number of physical buffersinto the single physical coalesced buffer if the total size of thevirtual buffers is less than the total size of the physical buffers. 8.The method of claim 7, wherein the determined number of virtual bufferscomprises a number of virtual buffers that have a total size associatedtherewith that is less than a predetermined size.
 9. The method of claim7, wherein the determined number of physical buffers comprises a numberof virtual buffers that have a total size associated therewith that isless than a predetermined size.